1. Rat-hepatic cells in suspension have been shown to have an endogenous respiration of 5.6+/-0.17 when suspended in 0.1 m-sucrose and 0.02 m-tris-hydrochloric acid buffer. The respiration in 0.25 m-sucrose and 0.02 m-tris-hydrochloric acid buffer is 30-40% less. 2. Potassium chloride (0.05 m) is slightly inhibitory and calcium chloride (0.0025 m) highly inhibitory to endogenous respiration of the hepatic cells in suspension. The cells do not respire in Krebs-Ringer phosphate buffer. 3. The respiration of the hepatic cells in suspension is stimulated by pyruvate, citrate, isocitrate, oxoglutarate, succinate, fumarate, malate and glutamate; there is no significant stimulation (or inhibition) by glucose, fructose, acetate and butyrate. In almost all the cases where stimulation was observed, it was found that the higher the endogenous respiration the lower is the stimulation.