CEM lymphoid cells expressing high levels of HIV-1 nef protein displayed a significant decrease in basal phosphatidyl-inositol 3-kinase (PI3-kinase) activity associated with immunoprecipitates with anti-p85 regulatory subunit. In contrast, chronically infected U937 monocytic cells displayed a significant increase in basal PI3-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 PI3-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 PI3-kinase activity and HIV-1 replication.L'activite phosphatidyl-inositol 3-kinase (PI3-kinase) a ete mesuree a partir d'immunoprecipitats obtenus avec un anticorps specifiquement dirige contre la sous-unite regulatrice p85. L'expression stable de la proteine nef diminue l'activite basale de la PI3-kinase dans les cellules lymphoides CEM non infectees. De maniere analogue, des cellules monocytaires U937 chroniquement infectees avec un virus HIV-1 delete du gene nef ont une activite basale augmentee par rapport aux cellules infectees avec un virus nef + . D'autre part, dans les cellules U937 chroniquement infectees avec le virus nef + , la wortmannine, un inhibiteur specifique de la PI3-kinase, inhibe la production de p24, ce qui suggere une correlation entre l'activite PI3-kinase et la replication virale.