CEM lymphoid cells expressing high levels of HIV-1 nef protein displayed a significant decrease in basal phosphatidyl-inositol 3-kinase (P13-kinase) activity associated with immunoprecipitates with anti-p85 regulatory subunit. In contrast, chronically infected U937 monocytic cells displayed a significant increase in basal P13-kinase activity in cells infected with HIV-1 nef compared to those infected with isogenic HIV-1 nef+. These findings suggest that HIV-1-nef expression is accompanied by a decrease in basal intracellular phosphatidyl-inositol 3-kinase activity and suggest that P13-kinase could be important for HIV-1 replication. Moreover, wortmannin, a potent in-vitro phosphatidyl-inositol 3-kinase inhibitor, can inhibit HIV-1 replication in U937 chronically infected cells. Together these results suggest a correlation between P13-kinase activity and HIV-1 replication.