Doctors and health charities have expressed concern about a conference which will examine the role of homeopathy in treating HIV.
The Society of Homeopaths said it wanted to promote an open debate
The event includes discussion of what have been described as "healing remedies" for HIV and Aids.
One of the speakers believes that the treatment, involving flower essences, can be used to halt the Aids epidemic.
But the event, which marks World Aids Day, has been criticised by doctors who say the treatment is not effective.
About 80 homeopaths and workers from HIV projects are gathering for the workshop in south London today.
It will include discussion about a remedy for HIV and Aids which is said to have been used in Africa for five years.
Medical charity Health Watch has criticised the event.
Its chairman said the number of Aids cases in Africa had been exacerbated by a refusal to accept scientific knowledge about the condition.
The Terrence Higgins Trust, which campaigns on HIV issues, said homeopathic remedies alone could not reduce the activity of the virus, nor halt the onset of Aids.
The Society of Homeopaths, which is organising the event, said it wanted to promote a constructive and open debate but it was not offering a cure.