Bone morphogenetic protein 7 (BMP 7), also termed osteogenic protein 1, a member of the transforming growth-factor superfamily, was examined for its efficacy in inducing reparative dentinogenesis in the exposed pulps of rat molars. To determine if the reaction was dose-dependent, collagen pellets containing 1, 3 or 10 microgram of recombinant BMP 7 were inserted in intentionally perforated pulps (10-12 pulps per group) in the deepest part of half-moon class V-like cavities cut in the mesial aspect of upper first molars. As controls, the collagen carrier (CC group) alone and calcium hydroxide (Ca group) were used as capping agents. All cavities were then restored with a glass-ionomer cement. Half of the animals were killed after 8 days and the other half after 28 days, by intracardiac perfusion of fixative. The molars were processed for histological evaluation by light microscopy. No difference in effect could be detected between the three concentrations of BMP 7 groups at either time interval. After 8 days, all groups showed varying inflammation, from mild of severe, and the Ca group demonstrated early formation of a reparative dentine bridge. At 28 days the CC group displayed irregular osteodentine formation, leaving some unmineralized areas at the exposure site and interglobular unmineralized areas containing pulp remnants. In the Ca-treated pulps, the initial formation of thick reparative osteodentine bridges that sealed more or less completely the pulp perforation was followed, in the deeper part, by irregular tubular dentine. In most BMP 7-treated specimens, the initial inflammation has resolved at 8 days and at 28 days heterogeneous mineralization or osteodentine filled the mesial coronal pulp. They also had complete filling of the radicular pulp by homogenous mineralization in the mesial root; this reaction was found in 11 teeth in the BMP 7 group, one tooth in the CC group an none of the Ca group. These results emphasize the biological differences the coronal and radicular parts of the pulp, and the potential of bioactive molecules such as BMP 7 to provide an a alternative conventional endodontic treatments.