There is provided, novel, transient, pro-drug forms of phenylbutazone and oxyphenbutazone having the following formula: ##STR1## wherein R represents a member selected from the group consisting of a C.sub.1 -C.sub.2 O-alkylsulfonyl group, an aryl(phenyl, p-tolyl, naphthyl)sulfonyl group, a nicotinoyl group, an iso-nicotinoyl group, a picolinoyl group, an N-protected naturally occurring amino acid residue, wherein the protective group on the amino group of the amino acid residue is removable via hydrogenolysis or hydrolysis, and an amino acid residue containing a C.sub.1 -C.sub.2 N,N-dialkylamino or a C.sub.4 -C.sub.6 cycloalkylamino group. ##STR2## wherein X and Y each represent a member selected from the group consisting of a hydrogen atom and a --OR.sub.1 group, with the proviso that either X or Y is a hydrogen atom and that R.sub.2 is a member selected from the same or different groups represented by R.sub.1 ; and wherein R.sub.1 represents a member selected from the group consisting of a hydrogen atom, a C.sub.1 -C.sub.2 O-alkylsulfonyl group, an aryl(phenyl, p-tolyl, naphthyl)sulfonyl group, a --CH.sub.2 COOM group, wherein M represents an alkali or alkaline earth metal (Na, K, Ca, Mg), a --CO-R.sub.3 group, wherein R.sub.3 represents a member selected from the group consisting of a straight or branched C.sub.1 -C.sub.5 alkyl group, a C.sub.1 -C.sub.2 alkoxy group, a phenyl group, a substituted phenyl group, whose substituents are selected from the group consisting of a 2,3, or 4-hydroxy group, a 2,3, or 4-acetyloxy group, and a 2,3, or 4-acetylamino group, a 2,3, or 4-pyridyl group, a 1,2, or 5-imidazolyl group, a residue of an N-protected naturally occurring amino acid, wherein the protective group on the amino group of the amino acid is removable via hydrogenolysis or hydrolysis, and an amino acid residue containing a C.sub.1 -C.sub.2 N, N-dialkylamino or C.sub.4 -C.sub.5 cycloalkylamino group. ##STR3## wherein X or Y represents a member selected from the group consisting of a hydrogen atom and a -OR.sub.1 group, wherein R.sub.1 is as defined above with the proviso that either X or Y is a hydrogen atom, wherein R.sub.4 represents a member selected from the group consisting of a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group, an aryl group (phenyl, styryl), a 2,3, or 4-methoxyphenyl group, and a -CH.dbd.CH.sub.2 group; and wherein R.sub.5 represents a member selected from the group consisting of a --OOC- R.sub.6 group, a ##STR4## group, and a -COOM group, wherein M represents an alkali or alkaline earth metal (Na, K, Ca, Mg), wherein R.sub.6 represents a member selected from the group consisting of R.sub.4 as defined above, with the proviso that R.sub.6 cannot be a hydrogen atom, and wherein R.sub.7 and R.sub.8 each represent a C.sub.1 -C.sub.3 alkyl group.The above-identified compounds exhibit anti-inflammatory activity in warm-blooded animals. Upon administration to warm-blooded animals, these compounds pass through the gastrointestinal tract and "cleave" in the bloodstream, thus releasing phenylbutazone or oxyphenbutazone in an anti-inflammatory effective amount at their therapeutic site or sites of activity.