This study investigated the effects of immersion of addition silicone rubber impressions in disinfectant solutions on the surface porosity of the resulting stone casts. Five brands of type 2 and 3 addition silicone rubber impression materials and one brand of type 4 dental stone were used. Impressions of a master die designed to simulate an abutment tooth were immersed in disinfectant for 30 minutes. The disinfectants used were 2% glutaraldehyde solution and 0.55% ortho-phthalaldehyde solution. The surface porosities of stone casts obtained from two brands of impression materials immersed in disinfectant for 30 minutes were determined. Results suggest that impression materials immersed in disinfectant solutions need sufficient time before pouring into dental stone.