The study found that DNA extraction and amplification was possible in all sperm samples even in the absence of spermatozoa due to a vasectomy. The same DNA profile was obtained for each man, regardless of whether the DNA sample was extracted from blood, prevasectomy semen samples, or postvasectomy semen samples. The findings suggest the importance of the use of markers specific for Y chromosome in sex crime cases, especially when spermatozoa are not found. In most rape cases there will be a small amount of the offender's DNA in the medium and large quantity of the victim's DNA. After informed consent, 105 men who desired vasectomy surgery were assessed. They agreed to donate semen samples both before and after the vasectomy, along with 5 ml of peripheral blood. This report describes the DNA extraction, DNA quantitation, and fragment analysis. 2 tables, 2 figures, and 24 references