DNA flow cytometry was performed on fine needle aspirates from the testes of 40 oligozoospermic of azoospermic men under investigation for infertility. The DNA distributions from men with increased FSH serum levels were all abnormal. The values were below the level of detection (or very low) with respect to both haploid (1c) and tetraploid (4c) cells, indicating reduced proportions of spermatids and primary spermatocytes. This confirms that increased FSH serum levels are indicative of severely damaged spermatogenesis. The findings of both normal and abnormal testicular DNA distribution in the large group of oligozoospermic men indicate that the presented method may be of importance for evaluating prognosis, and for selection of men for further investigation and therapy. Many azoospermic men showed normal testicular DNA distribution patterns, suggesting the value of DNA flow cytometry for selection of such cases for surgical treatment (epididymovasostomia).