The distribution of three radioactively labelled salicylate derivatives with low ulcerogenic activity was compared with that of acetylsalicylic acid (ASA) and salicylic acid using whole body autoradiography and liquid scintillation counting techniques in rats. The methyl ester of ASA (AME) was distributed in vivo very similarly to that observed with ASA and salicylic acid. AME is rapidly demethylated following absorption from the stomach and is subsequently converted to ASA and salicylate. Salicylate is the main metabolite produced from both AME and ASA, which specifically accumulates in inflamed tissues. The 3-methyl- and 6-methyl-substituted salicylic acids are not as rapidly absorbed as either ASA or salicylic acid and do not pass readily into the brain or bone marrow. These results show that the methyl (ester) group of AME (which adequately protects the gastric mucosa from damage caused by ASA itself) does not impair the quantity of pharmacologically active form of drug (salicylate and ASA) generated in vivo. However, insertion of the methyl group at the 3- and 6-position of salicylic acid markedly affects both absorption, distribution and pharmaco-activity of these acids.