The purpose of this in vitro study was to compare the efficacy of a new chemomechanical caries removal agent, Carisolv (MediTeam AB, Sävedalen, Sweden), with conventional slow-speed rotary instrument (bur). Fourteen extracted human molar teeth with deep dentine caries and no enamel coverage were selected for the study. Their laser fluorescence values were over 30 (DIAGNOdent; KaVo, Biberach, Germany). After the teeth were sectioned through the centre of the carious lesion, one half was removed with conventional drilling (bur); the other half was removed with Carisolv gel. Removal of carious dentine was continued until the lesion was deemed caries-free by visual and tactile criteria. The preparation time for each caries removal technique was also noted. The two halves of each tooth were fixed in 10% buffered-formaldehyde for 1 week. They were then decalcified, dehydrated and embedded in paraffin blocks for histological studies. After taking serial sections of 5 microm thickness, sections were mounted on glass slides, deparaffinized, dehydrated and stained with toluidine blue for observation under a light microscope. Each section was examined for the presence of bacteria. Complete removal of caries was achieved in 13 (93%) of 14 conventionally prepared teeth, and 5 (36%) of 14 chemomechanically prepared teeth (P < 0.05). Mean (+/-SD) time for caries removal was 272 s (+/-53.3) with Carisolv, and 116 s (+/-49.4) with drilling. The results of this study suggest that conventional rotary instrument (bur) was more effective than Carisolv in removal of carious tissue and also takes shorter time.