The chronic uremic condition was induced in male Wistar rats by long term maintenance of the animals following sequential sub-total and contralateral nephrectomies. Hepatic reticuloendothelial (RES) activity was estimated by non-invasive measurement of blood clearance rates and hepatic uptake of 99Tcm sulfur colloid administered intravenously. The blood half-time, and the blood clearance rate constants for normals and chronic uremics were 78 +/- 10 s and 49.5 +/- 5 s, and 7.51 +/- 1.04 x 10(-3) s-1 and 10.81 +/- 1.17 x 10(-3) s-1 respectively. The normal hepatic uptake rate constant was 9.03 +/- 1.25 x 10(-3) s-1, compared with a uremic uptake rate constant of 14.34 +/- 1.51 s-1. Measurement of total liver radioactivity upon termination, 15 min after injection, showed significantly increased total uptake in uremia, whereas no change in spleen radioactivity was observed. The clinical implications of these data are discussed.