External fixation of distal tibial fractures is often associated with delayed union. We have investigated whether union can be enhanced by using recombinant bone morphogenetic protein-7 (rhBMP-7). Osteoinduction with rhBMP-7 and bovine collagen was used in 20 patients with distal tibial fractures which had been treated by external fixation (BMP group). Healing of the fracture was compared with that of 20 matched patients in whom treatment was similar except that rhBMP-7 was not used. Significantly more fractures had healed by 16 (p=0.039) and 20 weeks (p=0.022) in the BMP group compared with the matched group. The mean time to union (p=0.002), the duration of absence from work (p=0.018) and the time for which external fixation was required (p=0.037) were significantly shorter in the BMP group than in the matched group. Secondary intervention due to delayed healing was required in two patients in the BMP group and seven in the matched group. RhBMP-7 can enhance the union of distal tibial fractures treated by external fixation.