The two surfactants tested, an alcohol ethoxylate (AE) and an alcohol ethoxy sulfate (AES), demonstrate both teratogenic and toxic effects in Xenopus laevis embryos and tadpoles. From acute tests and observations of malformations under light and electron microscopy, the AES produced less teratogenic and toxic effects than the AE, from which it differs only by the presence of a sulfate in the hydrophilic group of the molecule. The 72-h LC(50) was 4.59 mg/L for the AE and 6.75 g/L for the AES. The tissues most affected were the epithelia, particularly of the gills. As the AE exhibited ultrastructural alterations of mitochondria and narcotic effects, O(2) consumption was studied in treated tadpoles; results indicated collapse of the electrochemical gradient in mitochondria.