The aim of the study was to investigate the role of a testicular biopsy in the diagnosis and therapy of infertile men with a non-obstructive azoospermia. Overall, 70 testicular biopsies from infertile men were analysed. Samples were obtained by the "open testicular biopsy" method. After dissection, several pieces of the tissue were immediately immersed into the Sperm Prep Medium (Medi-Cult) and fixative (5.5% buffered glutaraldehyde). Tissue samples transported in Sperm Prep Medium were plunged into Sperm Freezing Medium (Medi-Cult) and were stored in liquid nitrogen for potential in vitro fertilization procedures. The tissue was also processed for semithin sections and transmission electron microscopy. Semithin sections from 8 infertile patients demonstrated regular testis structure and fully preserved spermatogenesis (control biopsies). In the remaining 62 cases, spermatogenesis was impaired and a variety of pathological changes could be seen: disorganization and desquamation of spermatogenic cells, spermatid or spermatocyte "stop", spermatogonia only, "Sertoli cells only" or tubular fibrosis. However, in 65% of cases (despite the above mentioned changes of seminiferous epithelium) foci of preserved spermatogenesis could be detected. These cases were classified as "mixed atrophy" of seminiferous tubules. In 63% of infertile patients, a successful extraction of sperm from the biopsy could be performed. In azoospermic patients, histological analysis of testicular biopsy proved to be very useful in terms of diagnosis as well as therapy, i.e. for further in vitro fertilization procedures.