The purpose of this in vitro study was to compare the efficacy of a new chemomechanical caries removal agent, Carisolv(TM) (MediTeam AB, Savedalen, Sweden) 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((R)); 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 mum 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.