Mice deficient in carbonic anhydrase II (CA II) were tested along with their normal littermates for susceptibility to seizures induced by flurothyl and loud sound at ages 10-180 days. In the flurothyl seizure model, CA II-deficient mice displayed increased resistance to clonic seizures from 32 to 90 days of age, whereas tonic-clonic seizures were suppressed at all ages. The mortality of CA II-deficient mice was significantly decreased at ages 19-40 days. The incidence of sound-induced seizures was very low and no difference between CA II-deficient and normal mice was found. The anticonvulsant effect of CA II deficiency appears to be dependent on seizure model and seizure type and to have age-specific characteristics.