This study was undertaken to investigate the effect of premedicants, diazepam and atropine sulfate in twenty surgical patients by measuring the Human Plasma Renin Acitivty. RENIN. RIA(Radioimmunoassay K for Angiotensin I) was utilized and the renin activity was expressed as the release of angiotenain I, ng. per ml. of plasma per hour. The sex ratio between male and female patients was 11:9, mean age 38,95+/-13.16 and average body weight 55.5+/-8.20kg. The value of the human plasma renin activity before administration of premedicants was 2.05+/-0.95ng/ml/hr. and at 60 minutes after administration of premedicante it was 2.21+/-0.82ng/ml/hr., and it's result was within normal limits. Consequently there was no significant change statistically in human plasma renin activity after one hour of premedications.