Nature 366, 716; 1993) state that Duesberg's claim that drug use rather than HIV is the cause of AIDS has been firmly rejected, but we do not agree. They rely in part on the Vancouver study (Lancet l3 March 1993) but Duesberg has pointed out that that study does not provide controls (verified drug-free AIDS cases). does not quantify drug use and ignores Zidovudine use. Garnett and Anderson also refer to one of us (J. S.) as a " television presenter" and use the phrase "non-expert opinion". J. S. has specialized in AIDS issues for seven years, and has made seven television documentaries analysing scientific knowledge about AIDS. Our work in preparing for the British network television documentary referred to involved consulting expert opinion from all the countries we visited as well as that of our special consultant Dr Harvey Bialy. The remarks by Garnett and Anderson about Bialy are totally unjustified. Bialy spent six years working in West Africa on the epidemiology of plasmidmediated antibiotic resistance among enteric pathogens, and in recent years has travelled extensively in Africa for WHO, UNESCO and UNIDO. He is an acknowledged expert on the implementation of biotechnology in Africa and has a wide knowledge of biotechnology-produced diagnostic tests.