The present study examines the effects of PCN congeners (PCN50 and PCN66) on zebrafish embryos. The embryos were exposed to different concentrations (20, 30 and 50 mu g/l) of the respective congeners by dissolving 0.08% acetone. The following endpoints were investigated (mortality, hatching rate, abnormalities and heart rate). No effect on survival was recorded for 20 mu g/l PCN congeners. On the other hand, embryos exposed to 30 and 50 mu g/l PCNs showed a significant reduction in survival rate. No developmental defects occurred with any of the congeners at the 20 mu g/l concentration. However, starting with 30 mu g/l, weak to very pronounced abnormalities (Lordosis, Kyphosis, disrupted axial body, tail defect, reduced heartbeat, and abnormal hatching) were observed depending on the congener and the concentration used. PCN66 has been shown to be more embryotoxic congener than PCN50. This demonstration of zebrafish responsiveness to PCNs early life stage toxicity coupled with the considerable information on developmental biology and genetics of zebrafish provides a foundation for future investigations into the mechanism of PCNs developmental toxicity. (c) 2007 Elsevier B.V. All rights reserved.