Excretion, organ distribution and metabolism of di(5-methylhexyl) phthalate (DMHP) were studied in male rats. Orally administered 14C-DMHP was rapidly absorbed, and 60 and 30%, respectively, of the radioactivity was found excreted into the urine and feces after 7 days. Biliary excretion amounted to about 15% of the dose after 4 days. No specific high concentrations were found in the organs and tissues. Four major metabolites were isolated by HPLC [high-performance liquid chromatography] from the ethyl acetate extract of the urine. All of these compounds were monoesters and determined as 5-hydroxy-5-methylhexyl phthalate, 6-hydroxy-5-methylhexyl phthalate, 5-carboxyhexyl phthalate and 3-carboxypropyl phthalate by spectral analysis (MS, [mass spectrometry], 1H NMR, 13C NMR, UV, IR, etc.). Unchanged DMHP and mono-5-methylhexyl phthalate (MMHP) were found, together with a small amount of phthalic acid, in the feces. MMHP and its glucuronide conjugate were detected in the bile. [Di(2-ethylhexyl)phthalate is a hepatocarcinogen in rats and mice.].