This randomized crossover out-patient study was designed to compare the antihypertensive effects of atenolol and pindolol. After a wash-out period of two weeks in pretreated cases, 107 patients with essential hypertension were given either atenolol 100 mg once-daily or pindolol 20 mg slow release (SR) once-daily. Both atenolol and pindolol lowered blood pressure over the 24 week period. The diastolic blood pressure reduction was significantly greater (p<0.01) with="" atenolol="" than="" with="" pindolol.="" before="">-blocker therapy, many patients had already experienced side-effects such as fatigue, sleep disturbances and dreams. This probably relates to the high sensitivity of the analogue scale used to assess side-effects, and to the high incidence of such symptoms in untreated patients. As the study progressed there was a reduction in the frequency of fatigue (p<0.03) and="" dreams="">p<0.05) in="" both="" groups,="" whereas="" sleep="" disturbances="" significantly="" increased="" under="" pindolol="">p<0.05) but="" decreased="" under="" atenolol="">p<0.05). the="" only="" important="" side-effect="" difference="" between="" the="" two="">-blockers was the higher incidence of sleep disturbances with pindolol which may be due to the higher lipophilicity of this -blocker.