The effects of formulation, particle size, coadministration of food, antacids, or antiulcer agents on the bioavailability of etodolac (ULTRADOL@, l,&diethyl-l,3,4,9-tetrahydropyrano [3,4-b]indole-I -acetic acid), a novel non-steroidal anti-inflammatory agent, have been evaluated in dogs and man. The effects of dosage regimen and/or repetitive dosing on bioavailability were also determined. In man, capsule and tablet dosage forms containing micronized etodolac were shown to have a bioavailability (AUC) equal to that of the reference etodolac solution. Etodolac from tablets and capsules was rapidly absorbed since only minor decreases in C,,, and increases in t, , , were observed compared to the etodolac solution. In a comparison of regular and micronized etodolac dosage forms, both in dogs and man, similar findings, i.e. no change in AUC but small parallel changes in C,,, and t,,,, were noted. Administration of etodolac with food had no effect on etodolac bioavailability in dogs but tended to cause a delay in its absorption. Coadministration of an antacid, magaldrate, or the antiulcer agent, sucralfate, had no effect on the bioavailability of etodolac in dogs, although with the latter, a significant reduction in C,,, was noted. In man, etodolac may be administered as a single bolus dose or in divided (b.i.d.) doses without any loss in bioavailability. With either regimen, on repeat administration for 7 days, no etodolac accumulation was noted.