We recently observed that prostaglandin E₂ (PGE₂)-mediated suppression of T cell functions could result from an attenuation of p59^fyn protein tyrosine kinase activity. The present study evaluated the effects of an adenylate cyclase agonist (forskolin) and antagonist (SQ-22536), as well as those of cAMP analogues (dibutyryl cAMP and 8-bromo- cAMP), on T cell p59^fyn kinase activity. The study allowed us to assess whether PGE₂-mediated activation of adenylate cyclase by itself or the elevation in intracellular cAMP levels is an integral event in the modulation of anti-CD3-linked p59^fyn activation in T cells. The experiments were carried out with splenic T cells from male Sprague-Dawley rats. A 30-50% suppression in the autophosphorylation and the kinase activity of p59^fyn in T cells incubated with PGE₂ or forskolin was observed. Pretreatment of T cells with SQ-22536 prevented significant PGE₂-mediated inhibition of T cell p59^fyn kinase activity. In contrast, no change in p59^fyn autophosphorylation and kinase activity in T cells treated with cAMP analogues was observed. These data suggest that PGE₂-mediated suppression of p59^fyn autophosphorylation and kinase activity in T cells is dependent on the activation of adenylate cyclase and independent of the elevation in cAMP levels.