A novel compound, LY83583 (6-anilino-5,8-quinolinedione), was found to lower basal levels of cyclic GMP (cGMP) in fragments of guinea-pig lung incubated in vitro. The lowering of cGMP was dose-related reaching a maximum of 72% at 5 X 10(-5) M. Basal levels of cyclic AMP (cAMP) were not lowered by LY83583. cGMP concentrations were also reduced in guinea-pig heart and cerebellum after incubation with LY83583. However, the drug did not alter the levels of this cyclic nucleotide in spleen. Exposure of lung fragments from sensitized guinea pigs to ovalbumin resulted in a marked increase in cGMP and cAMP. LY83583 prevented completely the accumulation of cGMP and attenuated the rise in cAMP. Similar results were obtained in rat cerebellum stimulated with kainic acid. The compound also blocked ovalbumin-induced release of slow reacting substance of anaphylaxis (leukotrienes) from guinea-pig lung. Subcutaneous administration of LY83583 to guinea pigs did not affect cGMP concentrations in vivo in lung, but the total amount of cGMP in spleen was reduced dramatically. This was accompanied by a marked splenomegaly. LY83585 did not inhibit lung guanylate cyclase. In fact, activity was increased in a cell-free preparation from guinea-pig lung. The mechanism by which LY83583 reduced concentrations of cGMP is presently unknown. Nevertheless, our studies suggest that LY83583 will be a valuable pharmacological tool to help elucidate the role of cGMP in biological events.