The effect of methyl prednisolone therapy (PM) was studied in 18 children with severe idiopathic nephrotic syndrome (NS). Eight patients were defined as "corticosteroid-resistant" because there was no response to treatment after a minimum of 4 weeks of 2 mg/kg/day of prednisone; 10 patients had a corticosteroid-dependent NS with frequent relapses which occurred under a high threshold dose of prednisone (1 mg/kg/day). Each patient received 4-6 pulses of 1 g/1.73 m2 methylprednisolone. Tolerance was generally good. PM therapy permitted a more rapid remission than oral prednisone (average 9 +/- 4 days vs. 22 +/- 9 days). Remission occurred in 5 of the 8 corticosteroid-resistant patients three of these 5 patients developed corticosteroid-dependent NS. For the children with a corticosteroid-dependent nephrotic syndrome, PM therapy did not affect the threshold dose of prednisone.