Contemporary developmental toxicity testing focuses on the evaluation of a variety of adverse developmental effects which include structural malformations, intrauterine death, growth retardation, and deficits in postnatal function. In the extrapolation of information from animal studies to humans, the most sensitive end point (i.e., the effect detected at the lowest dose) is used to establish the no observed adverse effect level (NOAEL). The approach is based on the assumption that a developmental effect seen in animal studies is predictive of a developmental effect in humans, but that the manifestation of the effect may vary from species to species. The testing procedures used also include an evaluation of maternal toxicity, which is important for determining that the proper dose levels have been tested. Many chemicals produce developmental effects at or near a dose that also produces minimal maternal toxicity. Developmental effects at maternally toxic levels are of concern since exposures may occur accidentally or intentionally. Doses below those causing maternal toxicity must also be tested, since developmental effects at these levels are of greatest concern. Finally, the lowest dose tested should establish NOAELs for maternal and developmental toxicity. In some cases, it may be possible to use the lowest observed adverse effect level (LOAEL), especially if the effect at this dose is near the limits of detection.