Dose-effect relations for barbiturates will be determined in rats using a behavioral discriminative motor control procedure. Using this technique, interaction and cross-tolerance between barbiturates and other agents will be evaluated as well. The development of barbiturate tolerance and the objective measurement of the abstinence syndrome will be determined by chronic administration and subsequent withdrawal while daily motor control testing is maintained. Similar studies on motor control will be done on rhesus monkeys. Blood drug levels will be measured by gas chromatography to correlate these levels with behavior as well as to evaluate the current metabolic status with respect to tolerance development (drug elimination rates).