Low-frequency pulsing electromagnetic fields (PEMF) are being used in nonunion healing at several centers around the world. Much debate exists about quantification of PEMF effects, especially in humans where no randomized studies have been performed. The results of a double-blind treatment of 32 consecutive patients treated with femoral intertrochanteric osteotomy for hip degenerative arthritis are reported. Roentgenographic evaluation and callus density measurements performed with an image analyzer showed a statistically significant difference between controls and stimulated patients (p less than 0.01). In this extremely homogeneous patient population, PEMF stimulation favored osteotomy healing.