The ability to predict the biological effect of complex waste mixtures from chemical characterization data was examined by comparing observed mortality to that predicted by a mathematical additivity model with literature LD50 values for the chemicals identified in the mixtures. Male F344 rats were exposed to one of ten samples of complex industrial waste by gavage. Seven of the ten waste samples caused death within 24 hours of administration at dosages ranging from 1 to 5 ml/kg body weight. Two of the seven lethal waste samples produced 100% mortality at a dosage of 2.5 ml/kg; another two waste samples produced 100% mortality at 5 ml/kg. The partial chemical analysis, although providing more extensive information on chemical composition than might normally be available for most complex waste mixtures, was not sufficient to distinguish lethal from nonlethal waste samples or to indicate lethal potency.