The purpose of the In Vitro Teratology Conference was to (1) reevaluate the need for and use of in vitro teratology assays, (2) examine the validation process for in vitro tests, and (3) discuss progress in the validation of in vitro teratology screens. Participants enthusiastically supported further development of short-term in vivo and in vitro systems both as pre-screens for developmental toxicity and as experimental systems to explore mechanisms of action of toxicants. The group strongly endorsed the development of an updated reference list ('gold standard') of known developmental toxicants and non-toxicants as essential to further progress in developing and validation pre-screening efforts. Independently, an expert group should further evaluate the performance characteristics for a validated pre-screen. The limits of mechanistic investigations need to be clearly defined. Finally, too few in vitro teratology pre-screens have been evaluated under multiple-laboratory conditions with common agreed-upon test agents to draw firm conclusions regarding the merit and reproducibility of in vitro teratology pre-screens.