Acute toxic effects on Salmo gairdneri, Poecilia reticulata, Daphnia magna, and the growth inhibition of Selenastrum capricornutum were measured for eight aromatic hydrocarbons. Toxicity measurements were carried out following the OECD standard guidelines modified as appropriate in order to prevent hydrocarbon loss by volatilization; the concentrations of the substrates in the test solutions were periodically measured by HPLC. The toxic responses were analyzed in terms of the n-octanol/water partition coefficients, by means of linear regression analysis, and in terms of five molecular properties simultaneously, by means of the partial least squares analysis in latent variables (PLS). The univariate and multivariate quantitative structure-activity relationship models obtained by the two approaches are compared and discussed.