Normal adult Sprague-Dawley rats received either a single or repetitive injection of the DNA precursor 3H-thymidine (3H-TdR). For autoradiography semi-thin sections were prepared 2 hr to 14 days after labeling. The majority of labeled cells noted in glomerular tufts were endothelial cells. Mesangial cells had a lower production rate. Podocytes revealed no evidence of proliferation. Bowman's capsule cells showed a higher labeling index than tuft cells at all times. Neither the urinary nor the vascular pole was found to be a proliferative zone for Bowman's capsule cells. The flash and repetitive labeling experiments demonstrated a constant rate of cell renewal of about 1% per day, resulting in a long life span for endothelial and mesangial cells as well as Bowman's capsule cells. These data provide a basis for cell kinetic studies in models of glomerular diseases.