• In one set of observations on 10 children with severe mental retardation, increased tendon reflexes, and resistance to passive motion, the dosage of zoxazolamine needed to produce a definite decrease in muscle tone was found to range from 30 to 140 mg. per kilogram per day. This dosage caused side-effects in eight, with vomiting in three. Respiratory depression occurred in one child who received 142 mg. per kilogram. In a second set of observations on 28 children with various psychomotor disorders, including muscular spasticity, doses of zoxazolamine sufficient to decrease the muscular tone significantly were given for 10 to 210 days. This caused clinical improvement in 15; there was improvement in such functions as sitting, crawling, walking, bathing, and dressing. The other 13 children showed no functional improvement despite the reduction in muscular tone.