Pharmacokinetic and physiological variables were measured in six healthy subjects after intravenous and oral administration of tolamolol. 2. After intravenous injection of tolamolol (20 mg), there was a biphasic decline both in plasma concentration and attenuation of maximum exercise tachycardia. First and second phase half-lives of plasma concentration were 7 min and 2.5 h respectively. WReduction of maximum exercise tachycardia declined from 32 beats/min at 2 h to 19 beats/min at 8 hours. Clearance of tolamolol from blood ranged from 0.8-1.41 min-1. 3. After the oral administration of tolamolol (100 mg), the average volume of distribution was 220.1 and plasma concentration half-life 1.8 hours. After ten eight-hourly doses of 100 mg there was no accumulation of tolamolol and the half-life of plasma clearance was unchanged. 4. Hydroxytolamolol was detected in plasma in two of six subjects after oral tolamolol. 5. There was a significant positive correlation between reduction in maximum exercise heart rate and logarithm of plasma concentration of tolamolol after both oral and intravenous administration.