The activity of phosphoinositide and adenylate cyclase systems of second messengers in rat brain under altitude chamber treatment (6000 m x 24 hours) were investigated. Selective suppression of each messenger system was achieved by pretreatment of rats with either lithium chloride or propranolol for 8 days. Consequences of this treatment and/or hypoxia were evaluated by orientation behavior and physical exercise test. Administration of LiCl caused reduction of phosphoinositide level; hypoxia (6000 m) causedfurther impairments in the second messenger content. There was synergism of interaction between between phosphoinositide and adenylatcyclase systems were demonstrated.