We studied the relationship of the administration and dosage of steroids to the development of avascular necrosis of bone in 168 patients who had had a heart transplantation (156 patients) or a heart and lung transplantation (twelve patients). One hundred and forty-one of the patients were male and twenty-seven were female. The average age was forty-five years (range, seven to sixty-six years). The average duration of follow-up was forty months (range, twelve to eighty months). Avascular necrosis developed in five patients (3 per cent). The femoral head was involved in three patients (bilaterally in two and unilaterally in one), the medial femoral condyle was involved bilaterally in one, and several sites were involved in the fifth patient. The avascular necrosis was diagnosed an average of five months (range, two to eleven months) after the transplantation. In order to evaluate the influence of the dosage of the steroids on the development of avascular necrosis of bone, the doses of prednisone and Solu-Medrol (methylprednisolone) at one week, one month, six months, and one year after the transplantation were calculated for each patient. There was no association between the cumulative dose of prednisone and the development of avascular necrosis. There was, however, a strong statistical association (p = 0.005), as determined with pooled two-tailed variance analysis, between the cumulative dose of Solu-Medrol administered in the first month after the transplantation and the development of avascular necrosis.