To elucidate the inhibitory effect of prostaglandin E2 (PGE2) on the generation of recombinant interleukin-2 (IL-2)-induced lymphokine-activated killer (LAK) activity, we have examined the association between cellular 3′,5′-cyclic adenosine monophosphate (cAMP) and cytolytic activity of 3-day IL-2-cultured murine LAK cells, i.e. at late phase of IL-2 induction, in the presence and absence of PGE2. The results indicate that, at the late phase of IL-2 induction, LAK cells retain their responsiveness to PGE2 inhibition, and the inhibition can be partially suppressed by additional IL-2 in proportion to the decrease in the ratios of stimulated to basal cellular cAMP lev