Evaluation of testicular biopsies from azoospermic men requires recognition of phases of germ cell maturation as organized architecturally within the seminiferous tubule, as well as distinguishing the inability to generate mature spermatozoa (germ cell aplasia or maturation arrest) from normal spermatogenesis, which may be associated with a reversible obstruction. While traditional fixatives (eg, Bouin solution) provide exquisite nuclear detail and preserve the architectural integrity of the seminiferous tubule, formalin fixation yields biopsies with relatively poor nuclear detail and frequent luminal sloughing of cells, making it difficult to assess sperm maturation. One clone of the anti-DOG1 antibody was recently found to be expressed in late (postspermatogonial) germ cells. We developed a dual stain including DOG1 and SF-1 to mark late germ cells and Sertoli cells, respectively, in both sloughed and intact cells. Consecutive testicular biopsies (N=28) from men with azoospermia were classified by hematoxylin and eosin morphology and stained with a dual SF-1 (Perseus)/DOG1 (Cell Marque) immunohistochemical stain. Histologic patterns included normal spermatogenesis (5 cases), hypospermatogenesis (5 cases), late maturation arrest (2 cases), Sertoli cell only pattern (15 cases), and extensive tubular hyalinization (1 case). Architectural disruption of seminiferous tubules with sloughing of cells into the lumens was noted in all biopsies, at least focally. SF-1 (nuclear) was expressed in sloughed Sertoli cells; DOG1 (cytoplasmic) in sloughed postspermatogonial germ cells (spermatocytes and spermatids). This resulted in two distinct immunophenotypes: SF-1(+)/DOG1(-) sloughed cells in cases with the Sertoli cell only pattern and SF-1(+)/DOG1(+) sloughed cells in all other histologic patterns (normal spermatogenesis, hypospermatogenesis, and maturation arrest). Because the rate of sperm retrieval is lower in men with the Sertoli cell only pattern, this immunohistochemical stain may assist pathologists in the proper interpretation of testicular biopsies, allowing better-informed decision making by patients and clinicians regarding the subsequent use of assisted reproductive technologies.