The goal of this project is to examine the interaction of severity of drug use and stage of HIV infection on cognitive function and cerebral metabolism. Both HIV infection and drug use have been shown to influence brain function, but the specific aspects of drug use (type of drug or severity of abuse) have not been well studied. Most studies of the effects of drugs in HIV infection have been with IV drug users, although this represents a small proportion of the overall HIV epidemic. Therefore it is important to investigate how drug use affects cognitive function and cerebral metabolism in non-IV drug users. This project will examine the independent and interactive effects of drug use and HIV infection on domains of cognitive function and cerebral metabolism. Subjects will be recruited from numerous local community sources and the sample will be stratified on the basis of severity of drug use and stage of HIV infection. Stage of infection will be based on the current CDC criteria (HIV-, Asymptomatic, and Symptomatic) and severity of drug use will be based on the Addiction Severity Index (low, medium, high). Subjects will receive an extensive neuropsychological examination, proton magnetic resonance spectroscopy, structured psychiatric interviews, and subjective symptom ratings. In addition to the Addiction Severity Index, urine samples will be obtained for analysis of drug levels. The data will be analyzed using factorial (3x3) ANOVA or MANOVA as well as multiple regression analyses. We will also follow these subjects longitudinally to study the effects of patterns of drug use on changes in cognitive function and cerebral metabolism. It is hypothesized that in addition to significant effects for severity of drug use and stage of infection, there will also be a significant interaction with the effects of drug use being greater with increasing severity of HIV illness.