Fifteen college swimmers, in midseason condition, swam 360 time trials after receiving 100 mg. of secobarbital, 14 mg. of amphetamine, or placebo on different occasions. After each trial a swimmer estimated his performance time and gave a detailed evaluation of his performance. Secobarbital significantly impaired performance, and amphetamine significantly improved it. The subjective data showed that secobarbital produced distortion in judgment; after taking secobarbital the swimmers thought their performances were unusually good, whereas in fact they were unusually bad. The effects of amphetamine on judgment were not conclusive.