Tolmetin, 1-methyl-(5-p-toluoyl)pyrrole-2-acetic acid, is a new, nonsteroidal, anti-inflammatory agent. After oral administration of tolmetin-14C to rats and mice, sequential microsamples of blood were obtained from the ophthalmic venous plexus via the orbital sinus. Plasma was collected after centrifugation, and microaliquots of each plasma sample were analyzed. The total radioactivity and thin-layer chromatographic assays used permitted quantitation of tolmetin, its dicarboxylic acid metabolite, and (by difference) all other metabolites collectively for each sample. Time-course data on plasma levels were obtained for individual rats and mice. The plasma elimination half-life of tolmetin was estimated at 0.67 +/- 0.13 hr (mean +/- SD) in male rats, 1.4 +/- 0.6 hr in female rats, 1.2 +/- 0.3 hr in male mice, and 1.0 +/- 0.0 hr in female mice. A one-compartment open model was used.