Three week old Sprague-Dawley rats, mean body weight of 50 gms, were injected intraperltoneally with 100 mg/kg of 1% lead acetate (PbAc) twice, 1 day apart. Control rats received 1% sodium acetate (NaAc). Renal plasma flow (RPF) and glomerular filtration rate (GFR) were measured using para-amino-hippurate and labelled inulin at 2 weeks post-injection. Blood lead concentration (Pb) and intra-arterial blood pressure (BP) were measured at the same time. Studies were repeated at 2 weeks post-injection in 9 week old adult rats, mean body weight 250 gms. (RPF/GFR ml/min/100 gm)Studies on young rats repeated at 4 weeks post-injection showed both RPF and GFR significantly reduced in the PbAc group compared to those receiving NaAc. No differences in BP were noticed between control and experimental animals in either group. Increased sensitivity of rapidly multiplying cells to noxious agents probably accounts for the observed difference.