The central effects of atenolol, a cardioselective beta-adrenoceptor antagonist, were investigated in six healthy men. Two flash-fusion threshold (2FFT), simple reaction time (SRT), digital copying (DCT), symbol-digit modalities (SDMT), and Gibson's spiral maze tests (GSMT) and mood rating scales for tension, alertness, depression, detachment, and anxiety were used. Each subject took 50, 100, 200, and 400 mg atenolol and identical placebo orally in a randomized, double-blind, crossover study and the psychomotor tests were performed at 0, 2, 3, 5, and 8 hr. 2FFT was prolonged at 3 hr after all doses and at 2 and 5 hr with 100, 200, and 400 mg. The maximum effect was achieved with 200 mg and mean 2FFT correlated with mean plasma atenolol concentration. SRTs were prolonged after all doses at between 2 and 5 hr. The DCT and the retest gain of the SDMT were both lower than after placebo at 2 hr with 100, 200, and 400 mg. The time taken to perform the GSMT was not altered by active drug, but the number of errors was lower at 2 hr with 100 and 200 mg. The self-rating mood scales showed a subjective decrease in tension 2 hr after 400 mg. The results show that atenolol exerts central effects in man.