IN A PREVIOUS paper (Chen and Portman1) a method was described for the quantitative titration of central-nervous-system depression. It is based upon the anticonvulsant action of a depressant, whereby the sedative, hypnotic, and anesthetic potency may be expressed in terms of the amount of a convulsant required to antagonize the depression. Sedation, hypnosis, and general anesthesia, expressed in terms of anticonvulsant effect, and the dose of a depressant were shown to follow the simple equation of mass action in three linear relationships. The slopes of the lines indicate the potency of an agent for the three stages of depression. The intersects give the minimal hypnotic and minimal anesthetic doses. In this paper there will be presented data on the joint central depressive effect of barbital and pentobarbital and that of pentobarbital and carbromal (bromodiethylacetylurea), as determined by their anticonvulsant activity. The two barbiturates were found to be additive, whereas