The results of a national HIV seroprevalence survey carried out in 1986/87 showed a 1% HIV seroprevalence in the South of Cameroon, which is higher than in the other regions of the country. We here demonstrate the presence of HTLV-I infections in the South of Cameroon with possible clustering of infection in some villages. Some evidence suggestive of the presence of HTLV-II was obtained. Sera from patients with onchocerciasis did not react on HTLV testing. No HTLV associated haematological or neurological syndromes were observed during this survey. Regarding the human immunodeficiency viruses, the HIV-1 prevalence varied from 0 to 3% in the different populations studied. None of the subjects was HIV-2 positive.