A seven-day short-term chronic toxicity test using 10-day old Daphnia magna is described as a possible alternative to the Ceriodaphnia life-cycle test. Five tests using sodium pentachlorophenate, conducted during the development of the method, gave test results similar to those previously reported for Daphnia magna chronic tests and comparable to Ceriodaphnia short-term tests conducted at the Environmental Monitoring and Support Laboratory in Cincinnati. This test can be completed in about half the time required for the Ceriodaphnia test and the neonates can be easily counted without the aid of a microscope.