Several acid and closely related non acid derivatives of 2-phenylthio- and 4-phenylthio-N-acyl phenylamines have been synthesized and tested in vivo, on the carrageenan RFE assay, and in vitro, on prostaglandin synthesis inhibition assay. Compound (XV c), bearing a propanoic acid substituent together with a p-chlorobenzoyl group situated on nitrogen atom in the 2-position, showed a 79% edema reduction (300 mg/kg p.o.) 6 hours after carrageenan injection, but no activity in vitro. The benzyl alcohols (XIV m) and (XIV n), on the contrary, inhibited PG synthesis; their lack of activity in vivo could be interpreted as the result of their oxidation to the inactive benzoic acids (XIV g) and (XIV h).