As little is known of the antihypertensive efficacy or renal haemodynamic effects of beta-adrenoceptor blocking drugs in the elderly we studied two such drugs, atenolol and nadolol, in elderly hypertensive patients. Ten patients took part in a placebo-controlled double-blind study of atenolol and 10 received nadolol in a single-blind placebo-controlled study. Treatment phases lasted 12 weeks for atenolol or 10 weeks for nadolol. Blood pressure, effective renal blood flow and glomerular filtration rate data obtained at the end of each treatment phase were analysed. Atenolol lowered mean arterial pressure (mean +/- s.e. mean) from 129.9 +/- 1.5 to 108.2 +/- 2.3 mm Hg (P less than 0.01) while it increased mean effective renal blood flow 512.5 +/- 86.6 to 646.0 +/- 116.1 ml min-1 1.73 m-2 (P less than 0.05). Nadolol reduced mean arterial pressure from 133.2 +/- 2.0 to 113.5 +/- 3 mm Hg (P less than 0.001) but reduced mean effective renal blood flow from 558.8 +/- 32.2 to 446.0 +/- 26.9 ml min-1 1.73 m-2 (P less than 0.05). Glomerular filtration did not alter significantly with either drug. We conclude that beta-adrenoceptor blocking drugs are effective antihypertensive agents in the elderly but have disparate effects on effective renal blood flow perhaps because of differences in cardioselectivity. These data suggest that comparative studies with thiazide diuretics and beta-adrenoceptor blocking drugs are warranted in elderly hypertensives.