In an attempt to clarify the indication and efficacy of the methylprednisolone pulse therapy (1000 mg x 3 times) for rapidly progressive glomerulonephritis (RPGN), 3 patients with the disease were carefully followed and the clinical course during and after the treatment were precisely analysed. According to the declination rate of reciprocals of serum creatinine (1/Cr), one patient were divided into the acute type (-1.00 x 10(-2) dl/mg/day or less) and the others into the subacute type (more than -1.00 x 10(-2) dl/mg/day). In the patient of acute type, renal biopsy revealed cellular crescent formation in 93.8% of glomeruli observed. One course of the pulse therapy resulted in a decrease in Cr from 3.0 mg/dl to 1.3 mg/dl and transformation of cellular crescents to fibrocellular or fibrous crescents. In the other two patients of subacute type, crescents were observed in 72.7% and 72.0% of glomeruli observed, and 87.5% and 38.9% of them were composed of cellular crescents respectively. Initial courses of the pulse therapy resulted in decreases of Cr from 3.5 mg/dl to 2.4 mg/dl and from 3.0 mg/dl to 1.4 mg/dl respectively. Additional courses, given because of insufficient reduction of Cr in the former, induced a further lowering to 1.3 mg/dl, and because of re-elevation of Cr to 2.2 mg/dl and remaining of cellular crescents in 20% in the latter, induced a decrease of Cr to 1.5 mg/dl and disappearance of cellular crescents.(ABSTRACT TRUNCATED AT 250 WORDS)