The concentrations of cyclic 3', 5'-guanosine monophosphate (cGMP) and cyclic 3', 5'-adenosine monophosphate (cAMP) in the cerebellar and cerebral cortex were measured during lidocaine infusion and during bicuculline-induced seizures in rats. The rats were divided into three groups: control, lidocaine (0.74 mg/min) and bicuculline (1.2 mg/kg). The lidocaine group was divided into four stages according to the EEG pattern; desynchronized, synchronized, seizure and recovery. At the desynchronized and synchronized stages, cGMP and cAMP concentrations in both cerebellar and cerebral cortex remained unchanged except for a modest decrease in cerebral cGMP at the desynchronized stage. At the seizure stage, cerebellar cGMP increased from 5.2 +/- 0.9 to 9.2 +/- 1.4 pmol/mg protein and cerebellar cAMP decreased from 8.9 +/- 0.6 to 6.9 +/- 0.6 pmol/mg protein. These changes in concentrations at the seizure stage returned to the control at the recovery stage. During bicuculline-induced seizures, cGMP and cAMP concentrations increased strikingly in both cerebellar and cerebral cortex. These results indicated that lidocaine-induced seizures were accompanied by significant changes in cerebellar cyclic nucleotide concentrations in rats.