To determine the quality of DNA isolated from actual casework specimens, its size was measured by agarose gel electrophoresis. The obtained information could be used to predict the stability of the DNA in the samples for restriction fragment-length polymorphism (RFLP) analysis. The bloodstains were selected from 100 different specimens submitted to the Office of the Chief Medical Examiner of the City of New York. The specimens were classified according to substrate (scrapings, plastic bags, synthetics, denim, and carpet) and according to a subjective evaluation of the condition of the stain (soiled, damp, or putrified) and to its size (small or large). To successfully analyze DNA RFLP there must be sufficient DNA present and the DNA isolated must be of sufficient quality, such as HMW. The results show that DNA can be reliably isolated from bloodstains deposited on evidentiary items which have an unknown environmental history and which have dried onto a variety of substrata. Further RFLP analysis of a selected number of these samples verified that the DNA was suitable for this type of analysis. 4 figures, 2 tables, 2 references. (Author abstract modified)