1,2-Dichloropropane was tested for chronic toxicity to the water flea, Daphnia magna, exposed in a 21-day assay under flow-through conditions. Groups of 20 daphnids (10/replicate) were exposed to mean concentrations of 0, 8.3, 15.8, 21.5, 39.5, or 72.9 mg/L of test material. Test water was maintained at 20.0 to 21.5 degrees Celsius, with 9.4 mg/L of dissolved oxygen and a pH of 8.1 to 8.3. The NOEL was 8.3 mg/L, and the LOEL (reproductive effects, immobilization, reduction in size, lighter coloration) was 15.8 mg/L, yielding a MATC of 11.4 mg/L. Flow-through toxicity tests were conducted with groups of 20 mysid shrimp from twoage groups (< 24 hours, and 3 to 4 days old)/concentration level. Animals were exposed for 96 hours to nominal concentrations of 4.92, 6.89, 10.88, 18.42, or 26.65 mg/L 2,4-dichloropropane. The 96-hour LC50 values for the two respective age groups were 24.79 (4.92 to infinity) mg/L, and >26.65 mg/L. The test water was maintained at 24 to 26 degrees Celsius, salinity was 20 to 21 ppt, dissolved oxygen level was > 6.4 mg/L, and pH was 7.6 to 7.8. The marine diatom, Skeletonema costatum, was exposed for 5 days under 14 hours light:10 hours dark to nominal concentrations of 0, 10, 18, 32, 56, or 100 mg/L 2,4- dichloropropane. The test water temperature was 20 + 2 degrees Celsius, pH was 7.5 to 7.6, and salinity was 30 ppt. High variability of measured concentrations in replicate flasks prevented calculation of EC values. The NOEC was 18 mg/L. Similar exposure of the freshwater green alga, Selenastrum capricornutum, to concentrations up to 1000 mg/L showed no effects. A neurotoxicity test was conducted in Fischer 344 rats orally exposed by gavage for 13 weeks to 0, 20, 65, or 200 mg/kg/day of test material. Early transient clinical signs, and minor decreases in body weight and temperature were noted, but no evidence of neurotoxicity was seen.