First reported in 1983, the human immunodeficiency virus (HIV) has been isolated from a high proportion (51 percent) of antibody-positive healthy persons and from almost all persons clinically ill with AIDS or AIDS-related conditions. To determine the length of the infective (carrier) state for the virus, blood specimens were collected from 23 antibody-positive donors 12 to 52 months after their original blood donation. All had detectable virus and it was concluded that a prolonged carrier state exists for this virus. The transmission of infection can occur through bloodborne agents and body fluids. Virus entry via mucous membranes is presumably facilitated in inflamed or traumatized tissue. Clinical changes seen in infected chimpanzees include decreased rate of weight gain and transient rashes. Through studies of transfusion-associated AIDS patients and serum specimens, it was determined that the incubation period for AIDS is long and may be even longer than current estimates. In a study of infected homosexual men to determine the proportion of AIDS development, between 23 percent and 26 percent developed AIDS-related conditions and between 7 percent and 15 percent developed AIDS. To date, no prognostic marker has been identified to differentiate those whose infection will progress to AIDS from those who will remain healthy. 1 table, 1 exhibit, and 14 references.