In 150 patients with oligozoospermia a testis biopsy of both testes was performed. In 76% the patients were 25-35 years old. Most of them had a sperm count less than or equal to 8.1 million/ml ejaculate (in the group of 0.3-1.1 million spermatozoa/ml ejaculate 32%, in the group of 1.2-8.1 million spermatozoa/ml ejaculate 43.3%, and in the group of 8.2-20.0 million spermatozoa/ml ejaculate 26.5%). The tissue of the testis was examined by the semithin slide technique. This method was preferred instead of the routinely used paraffin slide technique, because is semithin slides the different cells of the spermatogenesis as well as its pathological forms can be classified nearly to the limit of resolving power under a light microscope. Examples of histological pictures were given. In a statistical study especially the connection between tubules wall and cells of the spermatogenesis was examined. The tubule diameter which might influence the relation of the number of cells/tubule wall was connected. For all germ cells it could be observed, that the number of patients with the various germ cells decreased with thickening of the tubule wall. In this collective the high number of patients with a reduced number of spermatogonia was remarkable, as well as the number of patients with degenerating spermatocytes I degree and with pathological spermatids. These spermatids had especially abnormalities of the acrosom and of the nucleus. Furthermore the investigations revealed that the number of the germ cells in the tubules increase with higher spermatozoa density. But in the all cases the various numbers of this material showed only tendencies but no statistical significances.