This in-vitro investigation sought to identify the most effective softening agents for three commercial anterior resin composites (Prisma APH®, Brilliant® and Blend-a-Lux®) from four potential agents (75% ethanol, polyacrylic acid, acetone and acetic acid), selected as having close solubility parameter values to BIS-GMA. The Vickers microhardness test was applied to samples before and following a 180 s application of each agent. In addition, the degree of cavity enlargement following removal of resin composite restorations, aged by thermocycling, was assessed by image analysis. Using the same method the influence of both colour match and the 180 s application of softening agents, in the optimum chemical/material combinations, upon this was determined. Analyses of variance revealed that significant (P < 0·01) reductions in surface microhardness occurred when 75% ethanol was applied to Prisma-APH® and acetic acid to Blend-a-Lux®. Removal of restorations of all materials resulted in highly significant (P < 0·001) increases in cavity size. Application of either 75% ethanol to Prisma-APH® restorations or acetic acid to Blend-a-Lux® did not alter this result. Thermocycling only produced a significant (P < 0·01) (McNemar Test) deterioration in shade match of the Prisma APH® restorations but analyses of variance, for all materials, revealed that the observed changes in colour match had no significant (P < 0·05) effect upon the degree of cavity size enlargement. It is concluded that the application of softening agents to reduce cavity enlargement is not a viable clinical option.