3-Substituted-5-hydroxy(mercapto)alkylidene-rhodanine derivatives in which the 3-substituent is lower alkyl, cycloalkyl, alkenyl, phenyl, phenylalkyl, substituted phenyl or pyridylmethyl and having anti-arthritic activity are generally prepared from the appropriate 5-unsubstituted rhodanine by reaction with an orthoester followed by alkaline hydrolysis of the intermediate 5-alkoxyalkylidene rhodanine to give the 5-hydroxyalkylidene products or treatment of the intermediate rhodanine derivative with sodium sulfide to give the 5-mercaptoalkylidene products.