The present study was designed to evaluate the early aspects of the renal accumulation and intrarenal distribution of inorganic mercury in rats given a nontoxic 0.5 mumol/kg or a moderately nephrotoxic 2.0 mumol/kg intravenous dose of mercuric chloride. Each dose of mercuric chloride contained between 1.0-1.5 microCi 203Hg2+ in order to make it possible to follow the pattern for the intrarenal accumulation of inorganic mercury with standard gamma-counting techniques. Within the first 5 min after injection of either dose of mercuric chloride, about 70% of the dose of mercury was abstracted from blood. About 10% of the dose was in the combined renal mass, with the greatest fraction in the cortex. The liver contained about 5% of the dose. By the end of the first 3 h after injection of either dose, greater than 90% of the dose of mercury had been abstracted from the blood. At this time, about 8% of the dose was in the liver and more than 50% of the dose was found in the total renal mass. Again, the concentration of mercury in the renal cortex was greater than that in any other zone. The concentration of mercury in the outer stripe of the outer medulla also increased markedly over the first 3 h after injection, but was half that in the cortex. No change in the concentration of mercury was detected in the inner stripe of the outer medulla and inner medulla over the 3-h time-period. Findings from the present study indicate that the pattern for intrarenal distribution of mercury does not change significantly during the initial 3 h after injection of the moderately nephrotoxic dose of mercuric chloride. Normally, the concentration of mercury in the outer stripe of the outer medulla increases above that in the cortex sometime during the first 24 h after a low or moderately nephrotoxic dose of inorganic mercury. The present findings indicate that this shift occurs sometime after the first 3 h.