The induction of generalized tonic-clinic seizures in mice by the methylxanthine stimulant caffeine is described. These seizures are indistinguishable in quality from those induced by pentylenetetrazol (PTZ), and pretreatment with low doses of caffeine potentiates PTZ-induced seizures. Benzodiazepines inhibit caffeine-induced seizures with a rank order potency that parallels their affinities for the central nervous system (CNS) benzodiazepine receptor in vitro. Inosine, a purine that has recently been shown to be a competitive inhibitor of [3H] diazepam binding in vitro, antagonizes caffeine-induced seizures, while 7-methyl-inosine, a purine that lacks receptor binding inhibitory activity, has no effect on seizures. Since the benzodiazepines, inosine, caffeine, and pentylenetetrazol all competitively inhibit [3H] diazepam binding and have marked effects on inducing or antagonizing seizures, further study of this receptor-ligand system may provide additional insights that concern possible biochemical mechanisms of seizures.