The aim of this investigation was to compare the quantity of inflammatory cells in response to white and gray mineral trioxide aggregate (MTA) in subcutaneous connective tissue of rats. Fifty Wistar rats were used in this study. Polyethylene tubes were filled with gray or white MTA and empty ones serving as the control group were implanted into subcutaneous tissue and harvested after 7-, 15-, 30-, 60-, and 90-day intervals. Sections of 5 microm were stained with hematoxylin and eosin and observed under a light microscope. Inflammatory reactions were categorized as 0, none (without inflammatory cells); 1, mild (inflammatory cells < or = 25); 2, moderate (25-125 inflammatory cells); and 3, severe (more than 125 inflammatory cells). Statistical analysis was performed with the Kruskal-Wallis test. Both kinds of MTA provoked severe inflammatory reaction after 7 days, which significantly differed from control group (p < 0.05). However, there were no significant differences at any time period beyond 15 days (p > 0.05).