Nine laboratories participated in the extraction of DNA from 20 bloodstains and 20 semen stains using each protocol. All blood and semen stains originated from a single donor and were prepared under uniform conditions to permit the direct comparison of DNA yields and restriction fragment lengths. The extracted DNA from approximately 600 bloodstains and 700 semen stains were quantified by yield gel analysis and a slot blot hybridization technique. The extracted DNA was digested and restriction fragment length polymorphism (RFLP) from the blood and semen stains were evaluated with respect to (1) DNA extraction method, (2) gel length, (3) agarose type, (4) presence or absence of ethidium bromide in the gel, and (5) fragment sizes obtained from DNA isolated directly from the donor's liquid blood. This study demonstrates conclusively that high-molecule-weight DNA can be isolated using either organic or nonorganic DNA extraction protocols and that the resulting RFLP sizes are highly reproducible regardless of gel length, agarose type, or presence/absence of ethidium bromide. (Author abstract)