The effects on sleep of four beta-blockers, atenolol, propranolol, metoprolol and pindolol, were studied in a placebo-controlled trial. Drugs were administered in random order to 10 female volunteers who acted as their own controls. Subjects were tested five times, each test period lasting 10 nights (2 baseline, 2 low dose, 4 high dose, and 2 withdrawal). A questionnaire concerning subjective appreciation of the quality of the previous night's sleep was completed each morning. Night recordings of muscle tension, eye movement, heart rate and electroencephalogram were recorded on paper and magnetic tape. Analysis of the subjective questionnaires showed that recollection of dreaming and awakening in the night was increased by the three lipophilic drugs, propranolol, metoprolol, and pindolol. These results confirm reports in the literature but are contrary to those expected from considering the effects of noradrenaline on sleep. Analysis of physiological records confirmed subjects' reports that waking was increased by the lipophilic drugs. Dreaming (rapid eye movement sleep, REM) was reduced, as predicted from knowledge of the effect of noradrenaline on sleep. Increased awakening leads to an increase in remembered dreaming which explains the otherwise paradoxical results. Although atenolol had no effect on subjective measures of sleep this hydrophilic drug also reduced REM frequency, suggesting that either it has some central effect, or that REM reduction is due to a peripheral 'shielding' effect.