Chemicals in very small amounts were directly applied in the lateral hypothalamic area, where electric stimulation causes maximal positive reinforcement behavior. Effects on operant behavior rates of the chronic animals were measured. The independent variable was the chemical microinjection which followed each response; the dependent variable was the response rate. Response rates produced by carbamylcholine were significantly higher than those produced by NaCl; those produced by substances which chelate calcium were higher still and were counteracted when epinephrine, norepinephrine, or serotonin was added to the injected solution. Although individual animals sometimes failed to respond to an excitatory solution, a group of four rarely failed to place a chemical or solution correctly as yielding low, moderate, or high response rates. Final characterization of a chemical was determined by use of larger numbers and by statistical analyses which showed that findings related to carbamylcholine and to epinephrine, norepinephrine, and serotonin were repeatedly significant at 0.01 levels or better.