Frog Embryo Teratogenesis Assay — Xenopus (FETAX) is a 96-h whole embryo-larval assay designed to detect environmental developmental toxicants for use in ecological hazard assessment. FETAX offers several advantages in integrated biological hazard assessment including, time- and cost-effectiveness, technical ease, and versatility. FETAX has undergone extensive intra- and more recently interlaboratory validation with known mammalian teratogens and non-teratogens. Ecological hazard evaluations of contaminated sediments, waste site soils, and complex surface and groundwaters have also been performed. An integrated hazard assessment study using FETAX, the conventional, Pimephales promelas 7-d teratogenecity test, and an abbreviated P. promelas teratogenecity test utilizing the general FETAX protocol was conducted with specific reference toxicants and aqueous extracts of contaminated hazardous waste site soils. Results from the studies indicated that FETAX can be used as a component of a battery of bioassays designed to assess potential ecological hazard. Furthermore, the generalized FETAX protocol may be useful with other species in evaluating developmental toxicity hazard.