The environmental persistence of chlorinated hydrocarbon insecticides is posing a serious threat to the survival of several wildlife species. Sublethal effects, completely unrelated to the insecticidal properties of these chemicals, have contributed markedly to impaired reproduction in many species and to toxicity in neonatal animals. Considering the insecticide levels found in man, are these chemicals potentially dangerous to human infants and adults? Of special concern are the potential long-term, subtle effects of low concentrations of insecticides to which many persons are ordinarily exposed. These agents affect both the peripheral and central nervous systems. They markedly elevate hepatic enzyme levels, enhancing the biotransformation of many pharmacological agents as well as interfering with endogenous steroid biosynthesis and degradation. The DDT-like insecticides are potent estrogenic agents and some have shown teratogenic and carcinogenic activity. These aspects are discussed in relation to present levels found in humans and to possible adverse effects on perinatal and adult individuals.