Single, 1-h treatments of five stages of Fundulus heteroclitus embryos with Furanace solutions (2.0, 1.0, 0.5, and 0.25 ppm) resulted in no significant increase in either mortality or anomaly rates. We conclude that a 1-h treatment with Furanace may be safely used in the media supporting fertilized eggs. Chronic exposure of F. heteroclitus embryos in 2.0, 6.0, and 10.0 ppm solutions results in high mortality and anomaly rates.