A method for studying the in vivo accumulation of inorganic mercury along the nephron of Sprague-Dawley rats pretreated with a radiolabelled 0.66 mumol/kg dose of mercuric chloride is described in this article. Forth-eight hr after rats received the radiolabelled dose of mercuric chloride intravenously the kidneys of the animals were perfused in situ with a collagenase solution in order to dissect and isolate various readily assessable segments of the nephron and collecting duct. Three different categories of tubular segments were isolated; proximal convoluted tubules, proximal straight tubules and combined segments of the distal nephron and collecting duct. A group of isolated tubular segments were measured in length, drawn up and placed in counting tubes, and placed in a gamma counter for the determination of the content of inorganic mercury that accumulated in them during the 48 hr subsequent to the administration of the dose of mercuric chloride. In a separate set of animals, the intrarenal distribution of inorganic mercury was determined 48 hr after the intravenous dose of mercuric chloride was administered. Inorganic mercury accumulated mainly in the renal cortex and outer stripe of the outer medulla. In addition, the concentration of inorganic mercury in the outer stripe of the outer medulla was twice that in the cortex. The findings obtained with the isolated tubular segments revealed that most of the accumulated inorganic mercury in the kidneys of the rats was in the proximal tubule.(ABSTRACT TRUNCATED AT 250 WORDS)