PURPOSE: To measure the surface hardness and shear punch strength of six tooth-colored restorative materials before and after immersion in acidic and alkaline solutions. METHODS: Specimens were prepared from three resin composites; Ceram X, Filtek Supreme, Point 4, two polyacid-modified resin composites; Dyract, F2000, and one resin-modified glass-ionomer cement; Fuji II LC, immersed in distilled water for 24 hours at 60 degrees C, polished with silicon carbide papers up to 2000-grit and subjected to baseline measurement for Vickers hardness or shear punch strength. Further specimens were transferred to one of four aqueous media at 60 degrees C for a further 2 weeks; distilled water, 0.01 mol/L lactic acid, 0.1 N NaOH or coffee 15 g/500mL, washed, dried and tested for final hardness or shear punch strength. RESULTS: Data analysis using ANOVA and Tukey's test showed that the hardness and shear punch strength values were material and solution dependent. Regardless of the solutions; the hardness of F2000 was the highest and Fuji II LC the lowest; Point 4 and Filtek Supreme had the highest shear punch strength; Fuji II LC and F2000 had lowest. NaOH significantly reduced the hardness of all materials and completely dissolved the structure of Fuji II LC. Lactic acid and coffee significantly increased shear punch strength compared to baseline.