Comparative molecular field analysis (CoMFA) is used to relate ecotoxicological data with steric and electrostatic fields of chemicals forming an intentionally selected homogeneous set, the chlorophenols, for which reliable data are abundant in literature. Among these data, those concerning 16 different biological systems were selected, leading to predictive CoMFA QSAR in 14 of the cases. This is attested by cross-validation and bootstrapping, which also authorize the prediction of the chlorophenols toxicity values, when they are missing. The quality of obtained CoMFA models and the applicability of the method are discussed. The results are very promising, and they encourage further investigation into CoMFA in ecotoxicology.