Mice of the O'Grady strain which were inbred for susceptibility to audiogenic seizures were found to be more sensitive to pentamethylenetetrazol (Metrazol) convulsions than mice of the parent Swiss-Webster strain from which they were originally derived. A dose of 35 mg/kg Metrazol was required to produce a 50% convulsive response (CD50) in O'Grady mice and 50 mg/kg in the control parent strain. No differences in convulsive thresholds to Metrazol were obtained, however, between untreated Swiss-Webster mice and mice of the same strain made audiosuseptible by rubidium chloride intake or magnesium deficiency.