The purpose of the present study is to characterize the accumulation of inorganic mercury along the proximal tubule of the rabbit. New Zealand white rabbits were given a 0.5 mumol/kg dose of mercuric chloride along with 150 microCi of 203Hg. Forty-eight hours after the animals had been treated, individual segments of the nephron were obtained by microdissection. The segments of the nephron were measured in length and then were counted in a gamma counter to determine the percentage of the administered dose of inorganic mercury that had accumulated in them. There was significant accumulation of mercury along the proximal tubule during the 48 hr after the dose of mercuric chloride was administered. The S1 segment of the proximal tubule accumulated 0.000226 +/- 0.000031% (mean +/- SE) of the administered dose of inorganic mercury per millimeter tubule. The amount of mercury that accumulated in the S2 segment of the proximal tubule was similar to that in the S1 segment. By contrast, only half as much inorganic mercury accumulated in each millimeter of the S3 segment of the proximal tubule. No significant accumulation of inorganic mercury could be detected in pooled samples of various segments of the distal nephron. The findings in the present study indicate that the renal accumulation of inorganic mercury in the rabbit occurs mainly as a result of the accumulation of the metal in the proximal tubule, with the accumulation predominating in the S1 and S2 segments.