DNase I reduces the amount of soluble DNA by over 1,000 fold, while having virtually no effect on the sperm DNA remaining in the sperm head and inaccessible to the enzyme. Nuclease inactivation and sperm lysis then yield a soluble, pure male DNA fraction. An aliquot of soluble DNA is removed prior to nuclease addition to provide the victim's fraction. The standard method for purifying sperm DNA from vaginal swabs taken from rape victims is to selectively digest the victim's epithelial cells to solubilize the victim's DNA. The soluble DNA is then separated from the intact sperm by centrifugation. Vaginal swabs taken at determined time points following consensual sex and vaginal swabs taken from rape victims were processed using the nuclease method or the standard method. The nuclease method provides superior short tandem repeat profiles. The descriptions of materials and methods address nuclease protocol, the protocol for treating cell samples, standard selective lysis protocol, the Differex System, DNA quantitation, STR profiling, and cell samples. 2 tables, 2 figures, and 16 references