Stages of the spermatogenic cycle in human seminiferous tubules were evaluated in men with varied efficiencies of spermatogenesis to determine if the architectural arrangement of stages or the atypical cell types contributed to variation in sperm production rates. Testes were selected from men with low, intermediate, and high daily sperm production per g parenchyma (DSP/g). Round tubular cross sections were photographed by bright-field microscopy. Stages were identified for each cross section by two observers and the number of stages represented in each cross section was recorded. Number of stages per cross section in men with low efficiency of spermatogenesis were significantly (P < 0.05) fewer than men with intermediate and high efficiency of spermatogenesis. Further, the percentage of stages with atypical cell types in men with high DSP/g was significantly (P < 0.05) higher than men with low DSP/g. There was a significant relationship (P < 0.01) between the percentages of stages with atypical cell types per stage and number of stages per cross section. The atypical cell types appear to result from high density of stages per cross section in men with high DSP/g. There was no significant difference observed between groups for tubular volume, diameter, length, volume density, and volume density of seminiferous epithelium. However, a significant (P < 0.05) positive correlation between percent seminiferous epithelium per testis with DSP/g or with the number of stages per cross section was found.(ABSTRACT TRUNCATED AT 250 WORDS)