A 32-day test was developed at the Environmental Research Laboratory-Duluth for conducting early life stage (ELS) toxicity tests with fathead minnows Pimephales promelas. These test procedures were evaluated by using the prescribed methods to establish estimated maximum acceptable toxicant concentrations (MATC) for fathead minnows exposed to four previously untested organic chemicals. Toxic effects on early developmental stages demonstrated that larval growth and survival were the most sensitive indicators of toxic stress. Embryo hatch and larval deformities at hatch were the least sensitive indicators of toxicity. The estimated MATCs for fathead minnows exposed to hexachlorobutadiene, 1,2-dichloropropane, 1,3-dichloropropane and 1,2-dichloroethane lie between 6.5 and 13 micrograms per litre, 6 and 11 micrograms per litre, 8 and 16 micrograms per litre and 29 and 59 micrograms per litre, respectively.