Formaldehyde metabolism by the rat: a re-appraisal.

1. The metabolism of [14C]formaldehyde has been investigated in the male Sprague-Dawley rat. It is extensively oxidized to CO2 and formate, which is excreted in the urine. 2. Two radioactive compounds isolated from the urine of rats dosed with [14C]formaldehyde have been identified as N-hydroxymethylurea and N,N'-bis-(hydroxymethyl)urea, and shown to be urinary artefacts. 3. Previous studies of the metabolism of formaldehyde by rats have been re-appraised. Differences in the rate of oxidation of formaldehyde in various strains of rats result in the excretion of different urinary metabolites and, in some cases, formaldehyde. Excretion of formaldehyde leads to the formation of several artefacts depending on the components present in the urine.