This report presents the preliminary results from a (Q)SAR investigation of the acute toxicity to fish (fathead minnow) for a dataset of phthalate esters. A chemical set of 341 phthalates was compiled by using different searching engines. Their acute toxicity to fathead minnow was calculated with the ECOSAR and TOPKAT software. A good correlation between the predictions from the two programs was established (r2 = 0.81). The chemicals were classified initially into four groups on a basis of their predicted by ECOSAR LC50 values: 1) no reasons for concern (LC50 > 100 mg/L), 2) harmful (10 mg/L < LC50 < 100 mg/L), 3) toxic (1 mg/L < LC50 < 10 mg/L), 4) very toxic LC50 < 1 mg/L).