42 kidney biopsies from adults and children suffering from acute postinfectious glomerulonephritis were examined by light microscopy, immunofluorescence and electron microscopy. The biopsies were obtained within 9 weeks of the onset of the first clinical symptoms. The results show not only a range of variation in the histological picture (particularly in the accumulation of leukocytes in the capillary lumens, and in the degree of cell proliferation) but also different immunofluorescent patterns which we have called the "starry sky", "garland" and "mesangial" patterns. These patterns correspond to characteristic differences in the electron microscopic picture. The "starry sky" pattern (IgG, IgM and/or IgA, combined with C3) occurs mainly in the first weeks of the disease and is associated with an endocapillary-mesangial glomerulonephritis. This may turn into a "mesangial" pattern (mostly C3 alone) which is associated mainly with mesangial proliferation. Four types of immune deposits can be observed electron microscopically in all three patterns (subendothelial, subepithelial, mesangial and intramembranous), but their different quantitative distribution determines the characteristic picture. Subepithelial deposits (so called "humps") often considered characteristic of poststreptococcal glomerulonephritis play a dominant role in the "garland" pattern. The cases with a "garland" pattern often show strikingly high levels of proteinuria (greater than 5 g/24 hr). It is believed that in patients with postinfectious glomerulonephritis deposition of immune complexes of various composition is responsible for producing the described subtypes depending on their different distribution in the glomeruli. It seems possible that these subtypes have different clinical significance, something which could be confirmed by performing follow-up studies.