In a multicentre, single-blind, within-patient study, the effectiveness and tolerability of the fixed combination oxprenolol 80 mg + chlorthalidone 10 mg per tablet given once daily, compared to the well established b.i.d. schedule, has been investigated in forty out-patients with mild to moderate hypertension. After a two-weeks placebo wash-out, twenty patients were given 1 tablet b.i.d. of the fixed combination for 4 weeks and thereafter 2 tablets once-daily for a further 4 weeks; the remaining twenty patients were given the fixed combination in the reverse order. There was no significant difference in clinical response between the two treatment regimes, which were equally effective and well tolerated. However, patient compliance might be considerably improved with the once-daily dosage schedule of the fixed combination.