The effects of the common contaminants - soil, oil, gasoline, salt, acid, base, bleach, and detergent - on various forensically used genetic marker systems were studied. The predicted effects of the various contaminants on the proteins and the electrophoretic separations agreed with the observed results. A contaminant that affected protein conformation also adversely affected the integrity of the electrophoretic system, thus signalling an anomaly. It also was pointed out that the ideal control study for the effects of contaminants on genetic markers in evidentiary material is often provided to forensic scientists - that is victim's blood on victim's clothing and other substrata. The data presented in this paper support the validity and reliability of electrophoretic analyses of evidentiary material with respect to the contaminant issue.