The role of cow's milk protein intolerance in steroid-resistant nephrotic syndrome was evaluated in 17 children. Cow's milk was excluded from the diet for at least 14 days without changing previously ineffective predinisone dosage. Six patients with minimal change or mesangial proliferation went into remission 3 to 8 days after elimination of cow's milk. After a period of 2-3 weeks of remission, cow's milk challenge was positive in three patients. After one year on a cow's milk-free diet, two of six patients became milk tolerant and are in remission of NS, one of six became steroid-dependent, two of six are still unable to tolerate cow's milk and are in remission on a cow's milk-free diet and one of six children was lost from observation. The role of cellular mechanisms in steroid-resistant nephrotic syndrome is suggested.