A total of 394 cases of minimal lesion were reviewed and reassessed clinically and by laboratory investiga- tion, for 4 years from 1979 to 1982. Association with nephrotic syndrome is significantly higher in the cases with histologically normal-appearing mesangium than in the cases with mesangial proliferation. In 43% of the cases of minimal lesion, a minimal but prominent mesangial deposit of Immunoglobulin M with or without C3 deposit was found, and frequently accompanied with nephrotic syndrome, which is not sufficient to accept the condition as a specific disease entity such as "IgM Nephropathy" in our present study. Minimal lesion with a minimal but unmistakable deposit of lgA on the mesangium was noted less frequently and was accompanied or unaccompanied by nephrotic syndrome, a condition which call for an investigation clarify the characteristics and the extent of lgA(Berger's) nephropathy. Response to steroids in minimal lesion nephrotic syndrome was better in children and in the cases without mesangial proliferation, but was unrelated to either hematuria or immunoglobulin deposit. However, the cases with mesangial proliferation are significantly lesser in therapeutic response. Transformation to another morphological type of original glomerular change during follow-up was not observed in 4 available cases of minimal lesion nephrotic syndrome. Henoch-Sch nlein purpura was seen more commonly in children, and lgA(Berger's) nephropathy more commonly in adults.