Eight hours after intraperitoneal injections of 1.0, 2.0, and 4.0m equiv Li kg-1, the serum and brain lithium concentrations of rats were significantly greater after lithium orotate than after lithium carbonate. While little serum lithium remained at 24 h after injection of 2.0 m equiv kg-1 lithium carbonate, two-thirds of the 2 h serum lithium concentration was present 24h after lithium orotate. Furthermore, the 24 h brain concentration of lithium after lithium orotate was approximately three times greater than that after lithium carbonate. These data suggest the possibility that lower doses of lithium orotate than lithium carbonate may achieve therapeutic brain lithium concentrations and relatively stable serum concentrations.