Twelve healthy male volunteers received pyritinol 600 or 1,200 mg or placebo for 3 days according to a randomised, double-blind crossover design. On the 1st and 3rd days of each of the three treatment periods subjects completed a battery of psychological tests including Critical Flicker Fusion (CFFT), Choice Reaction Time (CRT), tests of memory and subjective drug effects at 1, 2, 4 and 6 h after dosing. Significant improvements in CFFT and CRT were found after pyritinol. There were no significant differences on the other tests, however, the observed enhancement in performance could be attributed to the effect of the drug.