The purpose of this investigation was to compare the tongue blade/Rodac plate assessment method, the Cariescreen (APO Diagnostics Inc., Toronto, Ontario, Canada) method, and a modified Cariescreen method for S. mutans assessment. Ninety-one triple tests were done on 23 children 1 to 4 years of age, and the S. mutans counts were compared. When all 91 tests were compared, there was agreement 86.3% of the time between the tongue blade/Rodac plate assessment method and the modified Cariescreen method. When the Cariescreen method was compared to the tongue blade/Rodac (Becton Dickins Labware, New Jersey) plate technique, there was agreement 72.2% of the time. Agreement tended to be at the low and high infection levels. When the Cariescreen and modified Cariescreen methods were compared with the tongue blade/Rodac method, most discrepancies were in the moderate range of S. mutans counts. Averages and standard deviations were 80.1 vs 32.1 for the modified Cariescreen method, and 86.9 vs 90.2 for the tongue blade/Rodac method. The linear product moment correlation coefficient was +.69. Overall, the modified Cariescreen method compared more favorably to the tongue blade/Rodac plate assessment than the Cariescreen method did.