It is known that changes occur in the renal glomerulus in toxemia of pregnancy, but what are extremely rate are the reports on a comparative study of the difference between the pure toxemia of pregnancy (called the pure type) and the superimposed toxemia of pregnancy (called the superimposed type). I have therefore clarified the difference between the morbidities by making observations of the two types mainly by transmission electron microscopy (TEM). The subjects were 19 cases of the pure type and 6 cases of the superimposed type, and light microscopic (LM) and TEM observations were made both after informed consent by performing a needle biopsy in the right kidney at cesarean section. By TEM observation, comparisons were made by giving 0-3 points for the findings in the endothelial cells epithelial cells, mesangium and basement membrane. By LM, the changes in the renal glomeruli in the pure type were classified roughly into the extracapillary type, endocapillary type and capillary type, but what was seen in many cases was a mixture of these changes. Regarding the morbidities in the superimposed type cases, my attention was attracted to adhesion with Bowman's capsule and a sclerotic image. In TEM observations, greater changes in the mesangium and basement membrane were seen in the superimposed type cases than in the pure type cases, compared with the changes in endothelial cells and epithelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)