Evidence for health effects at hazardous waste sites is scanty, largely because of problems with the studies and not because effects are not present. A few, well-designed studies with a priori hypotheses have shown excesses of birth defects, low birth weight children, liver damage, skin rashes, mood disorders, narcotic symptoms, and respiratory problems in populations around certain hazardous waste sites. Each of these studies have their own limitations in terms of internal and external validity. Recent advances in biomarker epidemiology hold promise for future studies of this important world wide problem.