Developmental models currently used by child behavioral toxicologists and teratologists are inadequate to address current issues in these fields. Both child behavioral teratology and toxicology scientifically study the impact of exposure to toxic agents on behavior development: teratology focuses on prenatal exposure and postnatal behavior development; toxicology on postnatal exposure and subsequent behavioral development. In general, the field of behavioral toxicology has underestimated, dismissed, or poorly evaluated the potential impact of psychosocial variables in determining an infant's or child's vulnerability to toxicants. Given the complexity of developmental processes, behavioral toxicologists and teratologists must adopt developmental models more complex than the "main effects" model currently in use. The more realistic interactive model, while better than the main effects model, is also inadequate since its elements are essentially static. Developmental toxicology must adopt a transactional model, or one that takes into account the ongoing transactions between individual biological and behavioral factors and the environmental contexts in which they operate. (An outline of a test battery formulated to link lead exposure to developmental delays is discussed in terms of five aspects that make it capable of addressing issues generated by the transactional model as applied to child behavioral toxicology.) (RH)