Dissociated human spinal cord cells were grown in monolayer cultures in the presence of serum from normal controls or from patients with ALS or other neurologic diseases. After 20 to 24 days, the levels of choline acetyltransferase, glutamic acid decarboxylase, and lactate dehydrogenase activities were determined in the cultures. On the basis of these biochemical measurements, there was no detectable difference between the effects of the three types of serum on the cultures.