To the Editor.— Hong Kong's current population is estimated at 5.4 million; about 90% are ethnic Chinese. It has a thriving tourist industry, with about 17 million arrivals and departures in 1984. Homosexual practice is illegal. Virtually no information regarding the number and sexual behavior of the homosexuals in this city is available. Prostitution is also illegal, although the service of prostitutes is readily obtainable in certain districts. Just how rigorously laws governing homosexualityand prostitution are enforced is not known. Because of the extensive exchange of visitors between Hong Kong and countries with high prevalence of acquired immunodeficiency syndrome (AIDS), human T-cell lymphotropic virus type III (HTLV-III) infections would be expected to be present in Hong Kong. We have therefore initiated a study to assess the frequency of HTLV-III antibodies among residents of this city. Study.— Ten groups of subjects were tested (Table). All serum samples were collected in