This proposal is concerned with phenomena related to the development of barbiturate tolerance, and some of the consequences of this tolerance. Six projects are to be carried out over the course of three years. These involve examining the effect of barbiturate tolerance development on barbiturate self-administration; quantification of barbiturate tolerance with dose-response curve shifts; determining if differential amounts of tolerance develop depending on the "level" of effect measured; carrying out parametric examination of barbiturate dose and frequency of administration on rate and amount of tolerance development; studying cross-tolerance between barbiturates and benzodiazepenes; examining acute barbiturate tolerance.