The bacterial catabolism of a technical formulation of alkylsulfonic acid phenyl esters employed as a general purpose plasticizer, Mesamoll, was elucidated. Two strains of the genus Rhodococcus were found able to utilize this substrate mixture as sole source of carbon and energy. Growth experiments along with enzymatic measurements indicated that both strains utilized the phenol that was released from the corresponding alkylsulfonic acid phenyl ester-probably by enzymatic hydrolysis catalyzed by esterases-via the ortho-pathway. By GC/MS analysis it was demonstrated that those alkyl chain homologues with substituents present at or close to the end of the aliphatic backbone (i.e., 2-tetradecylsulfonic acid phenyl ester) are degraded, while those with substituents close to the center of the alkyl chain (i.e., 7-tetradecylsulfonic acid phenyl ester) are rather persistent.