Since the Medical Research Council is better known for good science than good jokes, when they say "Bring your Wellington boots" I take it seriously. I buy a pair. I am off to Uganda to review the MRC Aids research programme in Entebbe as one of a team of scientists. In 1989, when Uganda was at the forefront of the Aids epidemic, this programme was set up to study the natural history of the disease in Africa.

Aids is a silent, slow-motion epidemic, but patience has paid off. Now, eight years later when a horrifying 20.8 million people in sub-Saharan Africa are HIV positive, about a million of whom are children, the research is showing some interesting results.

Day 1

An African Alliance aeroplane over the Sahara desert. In the early morning we land at Entebbe. After a few hours recovering we head for the Uganda Virus Research Institute where Jimmy Whitworth directs the MRC programme and coordinates field workers. We spend the afternoon touring the site. We meet the doctors and nurses who recruit and care for the patients. We visit the laboratories where scientists and technicians test blood samples and we stop off at the computer centre where programmers and data analysers are busy at their screens. Then in the evening, our work finished, we gather under a mango tree to relax.

Day 2

It is 7am (4am by my GMT internal clock) when we pile sleepily into the back of a Landrover and speed down the TransAfrican highway. We cross the equator with a mere nod. Jimmy's prediction that the only wild animals we will see on the road are taxi drivers turns out to be true. At Lukaya trading centre we turn off onto an unsurfaced track. Beautiful vistas of rural Africa appear and disappear as we negotiate the contours of the worst road I have ever traversed. Rain pours as we lurch from one muddy pool to the next. I realise what the Wellington boots are for.

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Three hours later we arrive at the study site, the rural subcounty of Kyamulibwa, a cluster of 15 self-contained villages with a population of 10,000, mainly subsistence farmers. HIV was observed in the area in about 1980, brought by truck drivers stopping off at Lukaya while travelling the highway from Kenya to Rwanda, Zaire and Tanzania. For the last step of its journey from town to village the virus probably then hitched a ride with local traders who regularly cycle back and forth laden with bananas.

We accompany the Ugandan field workers to the village they are surveying. Here they are meticulously gathering census information household by household and recruiting occupants into the study. They interview those who agree to participate and take a blood sample for a HIV test. An eye test is thrown in free of charge. From now on the participants have free access to the clinic and the whole family gets free medical treatment.

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This programme critically depends on good relations. Mutual benefit is the key. The MRC contributes towards road improvement, health education in schools, training of traditional birth attendants and free condom distribution.

Dilys Morgan shows us the clinic where rows of patients are waiting. Two doctors are busy with the checks, while in the tiny laboratory two technicians are processing blood samples. Dilys is Jimmy's wife. She spends three to four nights a week here in Kyamulibwa then heads back to Entebbe at weekends. "I've only failed to get through twice," she boasts. "And I hold the record for the fastest drive to Entebbe - 110 minutes." We are impressed. We leave late afternoon and three hours later we are on the hotel terrace eating fresh fish from Lake Victoria and BSE-free African beefsteaks under the spectacular southern sky.

Day 3

The staff present their results and plans. In Kyamulibwa 8 per cent of adults are HIV positive. This has not changed during the study period, but a recent fall in the virus levels in young men and women (aged 13 to 24) gives a glimmer of hope. Multiple sexual partners, itinerant lifestyle and poverty are the risk factors.

Now that this baseline information is established how is the work to progress? The Ugandan government spends $3 per head of population per year on health care and the average wage is $30 a month. But the drugs used to control HIV in Europe and the United States cost $1,200 a month for each person, so using these is out of the question. Here the emphasis is on prevention.

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Day 4

With our task completed I head for the TASO clinic. Noerine Kaleeba started TASO - The Aids Support Organisation - in 1987 after her husband died of Aids. It is an international success story. The Entebbe clinic is one of 17 in Uganda. It looks after 1,200 people on a shoe string. There are holes in the concrete floor, tiny hardboard-partitioned interview rooms and a cramped waiting area. But the place is alive with energy and optimism. Under the slogan "Living positively with Aids", it provides free counselling. The clinic is run by women and two-thirds of those attending are women. In a country where sexual inequality is ingrained, this is about empowerment. It has generated an openness towards HIV and Aids that is rare in Africa.

Dorothy H. Crawford, Professor of medical microbiology, University of Edinburgh.