The effects of straight chain fatty acids on seizures induced by picrotoxin and pentylenetetrazole were studied in mice. After i.p. injection capric, lauric, myristic, palmitic and stearic acid delayed the onset of picrotoxin-induced clonic convulsion in a dose-dependent manner. The survival time was also prolonged by the pretreatment with lauric, myristic, palmitic and stearic acid. However, the onset of the clonic convulsion induced by pentylenetetrazole was delayed only by lauric acid. The prolongation of the survival time was also observed only in the animals pretreated with capric and lauric acid. These results suggest that the straight chain fatty acids examined in the present study possess anticonvulsant activity in mice.