We previously reported the results of a randomized, double-blind 6-month trial of prednisone therapy in which 102 boys aged 5 to 15 years with Duchenne muscular dystrophy received daily doses of 1.5 and 0.75 mg/kg per day and were compared with those receiving placebo. The strength and function in both prednisone-treated groups improved equally and were significantly better than in the placebo group. To compare alternate-day and daily dosing of prednisone with respect to benefits and adverse side effects, the placebo group was started on alternate-day prednisone therapy, and the treatment group regimens were changed to equivalent doses of alternate-day prednisone without breaking the double-blind nature. At the end of 6 months, the group that was changed from daily to alternate-day therapy had declined in strength back to levels observed 12 months previously, at the start of daily therapy. The group in which alternate-day therapy was started showed a significant improvement in strength at 3 months, similar in magnitude to the response of boys treated with daily therapy. However, their strength declined significantly in the subsequent 3 months compared with boys who received daily therapy. The frequency of side effects was not significantly different for alternate-day therapy compared with daily therapy. We conclude that alternate-day prednisone therapy effectively increases strength but does not sustain the improvement to the same extent as daily therapy or mitigate side effects.