Recent information suggests that the central nervous system (CNS) is often impaired in HIV-infected individuals. The dysfunction of the CNS may be either a direct or an indirect result of HIV infection. One method to prevent HIV infection is to block entry of the virus into the cells of the body. Peptide T shows laboratory evidence of blocking the entrance of HIV into cells that are susceptible to HIV infection. Studies that have been done indicate that peptide T is nontoxic in the doses that are used in this study.