Cylindrical porous plugs (6.35 mm dia. 11 mm long, average pore size of 190 micron dia.) made of electrically conductive Co-Cr-Mo surgical alloy powders were implanted in the canine femur. An electrical stimulation device (mercury battery, 1.35 V, connected in series with a 150k omega resistor) was attached to all implants directly. The in vivo current was about 8 microA for the stimulated implants while no current was delivered for the control ones. After predetermined implant periods, tensile test specimens were made to measure the interfacial strength between bone and implants. Some samples were used for histological observations. The present results show that in vivo electrical stimulation substantially increased the strength of the union between porous implants and bone when compared to the controls up to 12 weeks. Histological observations show that the increased strength is mainly due to the increased new bone formation in the pores of implants. It was also observed that the fractional callus volume in the intramedullary canal for the stimulated samples retained more than the controls after reaching maximum at 3 weeks.