The aim of this study was to examine the changes to the weight and strength of restorative materials immersed in acetate media over a period of 16 weeks. Specimens of Fuji II LC and Fuji IX ((IC Int'l) and Compoglass (Ivoclar) were immersed in acetate buffer solutions containing calcium hydrogen orthophosphate at pH3 and pH7. Specimens in acetate media were maintained at 37'C with slight agitation. All solutions were changed and retained at weekly intervals and the specimens were weighed. After 1,2,3,4,8,12 and 16 weeks, batches of specimens were, subjected to shear punch testing. Seven batches of 12 samples were prepared of each material and for each pH. One-way ANOVA of she 3 materials and both pH's showed statistically significant differences between the groups. All specimecns gained weight at the commencement of the study (week I) and those in pH7 remained relatively unchanged thereafter. The specimens in p113 showed a gradual loss of weight after an initial gain as week 1. The shear punch strength of Compoglass peaked at week 2 and remained almost constant thereafter. There was a slight increase in shear punch strength observed in the other restorative materials at pH7 through weekcs I to 16. Fuli E LC and Fuii IX showed a considerably lower shear punch strength than Composlast. All soeciinen in vH3 solutions had an initial wei hi gain but a net weigtht lost was observed at the cuid of I6 weeka. Fuis1L(H and vH7 showe te inaxamum intial weijhI sin.