Absolute counts of germ cells were performed in 110 testicular biopsy specimens from 59 patients with either idiopathic infertility or varicocele and in a series of five autopsy specimens from age-matched controls. The tubular diameter, thickness of the tubular wall, and density of Leydig cells were measured. The following patterns were identified by germ-cell counts in the biopsy specimens: normal cell population, mild decrease in germ cells with normal ratio of cell types, advanced hypospermatogenesis with abnormal ratio of cell types, and Sertoli cell only. This sequence of progressive hypospermatogenesis was remarkably similar in both series. A separate category of maturation arrest was not recognized. Cell counts also correlated between right- and left-sided samples from the same patient in both series of biopsies. Reduction of tubular diameter, thickening of the tubular wall, and increase in Leydig cell density were often seen in severe stages of germ-cell impairment, although with an irregular distribution.