The absorption, excretion, and biotransformation of 14C-labeled pentaerythritol (PE) trinitrate was studied in man. The administration of a single sublingual dose was followed by rapid absorption and extensive biotransformation. Six drug metabolites were identified. Final excretion of the drug and its metabolites was almost totally through the kidney. Low levels of unchanged drug were present in plasma and urine. PE mononitrate was the major drug metabolite in plasma and urine. Glucuronides of PE trinitrate, dinitrate, and mononitrate were identified for the first time in man. PE trinitrate glucuronide appeared in plasma rapidly and about 8% of the dose was excreted in urine. Reversible and irreversible pathways are proposed for the formation of the metabolites. The reconversion of PE trinitrate glucuronide to PE trinitrate is postulated to explain the duration of drug activity and excretion.