Data from a number of sequential alternation experiments were factor analyzed to determine the number of common factors present. Three dependent variables (latency of convulsion, number of trials to six convulsions, duration of convulsions) were evaluated by three procedures: principal components solution with 1s in main diagonals, principal axes solution with largest r in the diagonals, principal axes solution with R2 in the diagonals. The results were similar; the presence of two factors was suggested in the latency and criterion measures (primary site stimulation and secondary site stimulation) and one in the duration data. A principal components factor analysis over the three dependent variables showed the presence of three factors, those observed in each of the separate analyses.