The present study examines the existence of clonogenic patterns in the proliferation and differentiation of spermatogonial stem cells in two species of non-human primates, the marmoset and the rhesus monkey. We developed a novel approach to detect proliferating spermatogonial clones in whole mounts of seminiferous tubules. Dual fluorescence labeling of bromodeoxyuridine and acrosin in conjunction with confocal microscopy allows the description of the clonogenic and spatial arrangement of proliferating spermatogonia at specific stages of the seminiferous epithelial cycle. Cross-sections of paraffin-embedded tissue were labeled by the same approach. For both monkey species we demonstrate the presence of proliferating spermatogonial clones of variable size at specific stages of the cycle of the seminiferous epithelium. Detailed analysis of the rhesus monkey reveals proliferating A_pale spermatogonia at stages VII and IX of the cycle of the seminiferous epithelium, and of proliferating B spermatogonia at stages II, IV, VI, and XII. Proliferating A_pale spermatogonia at stages VII and IX of the cycle are organized in pairs or quadruplets. B₁ spermatogonia appear as quadruplets or eight-cell clones, and B₂ spermatogonia as 8- or 16-cell clones. We conclude that spermatogenesis in the rhesus monkey is initiated by two divisions of duplets or quadruplets of A_pale spermatogonia: a first division at stage VII, after which the clones of A_pale spermatogonia separate, and a second division at stage IX, which leads to clones of B₁ spermatogonia as well as pairs and quadruplets of A_pale spermatogonia replenishing the seminiferous epithelium to maintain the original size of the A spermatogonial population.