Interictal epileptiform EEG activity was recorded in 10 rats with pentylenetetrazol-induced generalized seizures and in 10 rats with cobalt-induced partial epilepsy. Thirty spikes were averaged for each rat, and morphological parameters of the average waveform (such as amplitude, duration, and 1st derivative of the rising and falling spike deflections, and sharpness at peak) were measured. Pentylenetetrazol rats showed significantly higher and longer spikes than cobalt animals with a faster 1st derivative of both deflections; sharpness at peak was also higher in this group. The second spike deflection was higher and longer than the first in both groups of animals. The conclusion is that morphological spike parameters, when studied in groups of animals not treated with antiepileptic drugs, show significant differences between different experimental groups, probably reflecting a different cortical involvement and/or different epileptogenic mechanisms. The study of spike morphology can be extended to human epilepsy if etiopathogenetically homogeneous and untreated groups of patients are considered.