Force-fed rats were injected with a single dose of an organic mercurial compound, N-(β-hydroxymercuri-γ-methoxy) propyl- N′-succinylurea), and their 24-hour urine samples were collected for 10 days following the injection. The urinary excretion of inorganic and organic compounds was altered greatly. In spite of these alterations the total determined cations and total determined anions remained essentially constant as the result of the following: An increased excretion of sodium plus potassium on day 1 was accompanied by a decreased excretion of ammonium ion. An increase in the excretion of chloride on day 3 was accompanied by an increase in ammonium ion. A retention of sodium on days 3–5 was accompanied by an increased excretion of ammonium ion. The excretion of total and inorganic phosphate and total and inorganic sulfate remained essentially constant. There was an increase in the total 10-day excretion of creatine, glucose, citric acid, α-amino acid nitrogen, arginine, guanidinoacetic acid, undetermined nitrogen, titratable acidity, potassium, and hydrogen ion and a decrease of uric acid. The 10-day excretions of creatinine, urea, ammonia, sodium, total nitrogen, chloride, organic acids, sulfate, and phosphate were essentially unchanged. Kidney tissue from rats that had been given a dose of the mercurial compound had normal amounts of creatine, arginine, and transamidinase activity. Serum levels of creatine, creatinine, arginine, glucose, sodium, and potassium also were not altered. A mechanism for the mercurial-induced alterations of the urinary excretion of chloride, sodium, potassium, and ammonium ions in the normal force-fed rat has been discussed.