Thirteen rabbits received parenteral injections of human serum albumin (HSA) in regular doses and intervals during 6-32 seeks. The antigen load elicited immune responses of variable degree, giving a good correlation with the extent and quality of immune complex (IMC) deposition, as shown by immunological methods, electron and fluorescence microscopy and by histoautoradiography. Morphology of immune deposits (IMD) depended on the composition of the IMC and produced a continuous scale of glomerular involvement, ranging from minimal and focal to massive and diffuse deposition. Probable rudimentary traces of IMD were apparent in the ultrastructure even in animals with negative results of both immunological and immunfluorescence examinations. The relationships are discussed between experimental IMC-induced glomerulopathy on the one hand, and some problems of development and bioptic evaluation of human glomerulonephritis.