The untreated sour water from a coal‐gasification process has been examined for toxic and teratogenic effects on the embryos of the amphibianXenopus laevis.Embryos were exposed to varying concentrations of sour water, and the number of deaths and abnormals as well as motility, pigmentation, and stage of development were monitored. Increases in toxicity and teratogenicity were directly related to both concentration and time of exposure. The sour water also caused a reduction in motility, pigmentation, and rate of embryonic development.