The effects of pertussis toxin, forskolin, and cAMP analogues on the antinociceptive action of nicotine were examined to investigate the possible involvement of adenylate cyclase and G-proteins in nicotine's antinociceptive effect. Intrathecal injection of pertussis toxin (0.25 and 0.50 micrograms) in mice inhibited nicotine-induced antinociception in the tail-flick test. The effect of the toxin was dose and time dependent. Forskolin, a potent adenylate cyclase activator, and 8-(-4-chlorophenylthio) adenosine-3':5' monophosphate, cyclic (8-CPT-cAMP), a cAMP analogue, inhibited the antinociceptive effects of nicotine in a dose-dependent manner. EGTA reversal of 8-CPT-cAMP's inhibitory effects suggests that calcium may to be involved. These data implicate the possible involvement of a G-protein and a second messenger system (activation of a cAMP-dependent protein kinase and increase in cyclic AMP levels) in nicotine-induced analgesia in mice.