Proliferation of normal T lymphocytes is impaired by human immunodeficiency virus (HIV) proteins. In this paper, we demonstrate important parts of this mechanism. Initially, HIV-induced impairment of proliferation was shown to be an active process involving induction of protein tyrosine kinases in both CD4 and CD8 T cells. Furthermore, the impairment of cell proliferation was demonstrated to be linked to induction of the inhibitory protein kinase A (PKA) pathway by HIV proteins. This induction of PKA was accompanied by an increase in intracellular cAMP, which is necessary for the activation of PKA. Finally, increases in cAMP/PKA activity were shown to induce biochemical changes that impaired proliferation when cells were stimulated with phytohemagglutinin. This was demonstrated by showing that (i) agents, other than HIV proteins, that increase cAMP/PKA activity (cholera toxoid and 8-bromo-cAMP) also decreased T-lymphocyte proliferation; (ii) exposure of lymphocytes to HIV or cholera toxoid led to decreased membrane activity of the proliferation promoter protein kinase C upon stimulation; and (iii) agents that reduced cAMP generation neutralized the effect of HIV proteins and restored lymphocyte proliferation. These studies show that the HIV-induced augmentation of cAMP/PKA activity may be a key part of the mechanism responsible for all or part of the HIV-induced anergy of T lymphocytes.