Presumptive tests are a necessary part of the analysis of eviden- tiary materials recovered from crime scenes. Given that some presumptive tests can interfere with conventional genetic marker analyses, such that they yield no or inconclusive results, deleterious effects might also occur in the STR analysis of body fluid stains. As DNA typing gains widespread imple-mentation in the forensic science community, it is essential to understand the effects of the most common presumptive test reagents.2