Seeman and O'Brien1 have reported that the mean sodium, potassium-ATPase activity in the red cell ghost membranes of 6 schizophrenic patients (79.1 mµ;moles ATP split/h/mg dry weight) was significantly greater than in four normal subjects (35.2). Total ATPase was also greater among patients than controls, although the difference in the residual or magnesium-dependent fraction was said to be statistically insignificant. When enzyme activity is expressed in this way, small differences in ghost weight could result in large differences in activity. For this reason it would appear more valid to express sodium, potassium-ATPase as that percentage of the total ATPase activity which is activated by sodium + potassium. When the data for schizophrenic and normal subjects are calculated in this way (sodium, potassium-ATPase × 100/total ATPase), the result for the normals is 16 per cent and for the schizophrenics 24 per cent, a much smaller difference.