AbstractThe effects of metal‐contaminated sediment extracts and a reference toxicant (zinc sulfate) were determined by examining the developmental morphology, growth and mortality of exposed fathead minnow (Pimephales promelas) and frog (Xenopus laevis) embryos. Sediments from two contaminated stream sites were extracted with reconstituted culture water at various pH values for 24 h. Developmental toxicity tests were performed using the frog embryo teratogenesis assay‐Xenopus(FETAX) protocol. The results suggest that Zn was the major developmental toxicant in the sediment extracts. The measured Zn concentration in the sediment extracts that caused malformation in 50% of the fish embryos (EC50) was 0.5 to 1.4 mg/L (normalized to 100 mg/L hardness). EC50 values for the reference toxicant tests were 0.6 and 0.8 mg/L Zn. The frog embryo EC50 for the extracts ranged from 2.2 to 3.6 mg/L Zn and was 3.6 mg/L Zn in the reference toxicant test. In 67% of the tests, malformation was a more sensitive endpoint than growth inhibition. Mortality was the least sensitive endpoint, that is, the LC50s in the reference toxicant tests were 3.6 mg/L Zn for the fathead minnow and 34.5 mg/L for the frog. The extraction procedure may be useful for determining potential toxicity in the event metals are leached from aquatic sediments by dredging or acidificat