A series of neurophysiological tests was performed on Long-Evans hooded rats treated with either 2-, 3- or 4-methylpyridine at dosages of 100mg/kg, approximately 1/2 the i.p. LD50. The tests contained measures of sensory function (paired pluse flash evoked potentials, pattern reversal evoked potentials, brainstem auditory evoked responses) and cerebral excitability (pentylenetetrazol (PTZ) seizures and hippocampal afterdischarges). In general, rats treated with 2- and 3-methylpyridine were more affected than those treated with 4-methylpyridine. The changes observed were in many ways similar to those seen following administration of depressant compounds: increased latency of evoked potentials and increased latency to PTZ seizures. Not all findings, however, were consistent with previously observed patterns of CNS depression.