Infusion of d,l-propranolol in both anesthetized and conscious dogs caused decreases in heart rate (HR), plasma renin activity (PRA), and plasma aldosterone. There was no consistent change in mean arterial blood pressure, plasma renin substrate concentration, packed cell volume, plasma potassium, or plasma sodium concentration following the infusion of propranolol. In five conscious animals, infusion of propranolol (1 mg/kg followed by 0.47-0.65 mg kg-1 h-1) reduced HR from 117.6 +/- 4.0 beats per minute (mean +/- SE) during control periods of 73.2 +/- 2.0 beats per minute (P less than 0.005) 90 min after the start of infusion. PRA decreased from 9.97 +/- 1.79 ng ml-1 h-1 during control periods to reach 1.50 +/- 0.42 ng ml-1 h-1 (P less than 0.005) at the end of the 90-min infusions. Plasma aldosterone also decreased during this time from 17.60 +/- 1.93 ng% during control periods to reach 6.64 +/- 0.98 ng% (P less than 0.005). The data suggest that propranolol at the dose administered suppresses renin and aldosterone secretion in unstimulated dogs. They suggest also that beta-receptor activity contributes to basal renin release.