Carisolv is a minimally invasive method for softening and removing dentine caries. A new, modified Carisolv gel has been developed in order to optimise the efficiency if its chemical caries dissolution. The aim of the present study was to compare the caries removal efficiency of the original gel with that of the new gel, which contains almost double the concentration of sodium hypochlorite. Ten dentists treated 202 cavities in 170 patients; 104 cavities were randomised to the new gel and 98 to the original gel. Their mean treatment times for caries removal were 6.7+/-4.1 min and 7.6+/-4.2 min, respectively ( P>0.05). In close-to-pulp lesions, constituting 32% of the cavities, the mean times for caries removal were 9.0+/-7.0 min and 11.6+/-4.4 min for the new and original gels, respectively ( P<0.01). Questionnaires revealed that 81% of the patients preferred chemomechanical treatment to drilling. In conclusion, the improved efficiency of the modified Carisolv gel did reduce the time for caries removal in deep lesions. However, it still needs more time than conventional drilling.