Low-dose cyclosporin(CsA) therapy combined with prednisolone was performed in 10 adult patients with frequently relapsing minimal change nephrotic syndrome(MCNS). Oral CsA was administered at the dose of 1-3 mg/kg/day(50-150 mg/day) in combination with preceding prednisolone(32.5 +/- 13.1 mg/day). The whole blood traugh concentration of CsA was maintained at the level of 50-100 ng/ml (ranging in 35-160 ng/ml, mean: 68.0 +/- 42.8 ng/ml), and the therapy was continued for 31.7 +/- 12.7 months. The urinary protein excretion, serum total protein, albumin and total cholesterol significantly improved after treatment. The serum creatinine increased slightly at 3-6 months after treatment, but decreased to within the normal range thereafter. The frequency of relapse and the ratio of the complete remission period to the total observed period were compared between the pre-treatment period(36.6 +/- 42.5 months) and post-treatment period(31.7 +/- 12.7 months). The frequency of relapse was significantly decreased after CsA treatment(2.3 +/- 1.5 times/year-->0.7 +/- 0.7 times/year, p = 0.02). The ratio of the complete remission period to the total observed period was increased significantly after CsA therapy(61.7 +/- 24.3%-->88.6 +/- 14.5%, p = 0.01). Thus, the low dose cyclosporin(CsA) therapy combined with prednisolone was an effective treatment for adult MCNS patients who relapsed frequently under conventional prednisolone therapy.