All of the samples in this study were analyzed by the RFLP /variable number of tandem repeats (VNTR) method developed at the Federal Bureau of Investigation (FBI) Laboratory. The environmental factors examined included sunlight, temperature, different substrates and durations of time; cotton, nylon, blue denim, glass, aluminum, and wood comprised the substrates. In addition, biological contaminants covering bacteria, yeast, and other body fluids as well as nonbiological contaminants such as gasoline, bleach, sodium hydroxide, soil, motor oil, detergent, phosphate salt, glacial acetic acid, and microorganism were prepared to simulate commonly encountered contaminants. The validation studies showed that evidentiary samples exposed to a wide variety of environmental influences can yield DNA that will produce a valid and reliable RFLP pattern. Furthermore, a RFLP pattern could not be obtained if the DNA were adversely affected. The DNA profiles produced from the test samples were consistent with those of the control samples, otherwise no profiles were produced. These results suggest that DNA analysis by RFLP is a reliable method for the characterization of body fluid stains. 12 figures, 1 table, and 12 references (Author abstract modified)