Rats were injected with 1 of 3 solutions, and then given 200 shock-avoidance trials in a shuttle box with light as the CS. On several measures of acquisition of the avoidance response, rats receiving .0125 mg. adrenalin per 100 gm. body weight scored significantly higher than rats receiving .25-.50 mg./100 gm. or placebo conrtols. The apparent nonmonotonic relationship between dosage and learning may result partially from the pathological effect of large doses of adrenalin. (PsycINFO Database Record (c) 2006 APA, all rights reserved)