The effect of single oral doses of penbutolol (40 mg) and propranolol L.A. (160 mg) on psychomotor performance of 12 normal individuals has been investigated. Subjects were randomly administered penbutolol, propranolol L.A. and placebo according to a double-blind, three-part cross-over design. At 3 h post-dosing both penbutolol and propranolol L.A. significantly increased (P less than 0.001) complex reaction times when compared to placebo. By 24 h post-dosing the mean complex reaction times for penbutolol and propranolol L.A. were not significantly different from placebo.