Research was undertaken to determine whether improvements were needed to increase the reliability of acute toxicity methodologies for mysid and juvenile Atlantic silverside waste characterization tests for municipal sewage sludge. Three new acute bioassays using mysids, larval fish and calanoid copepods were designed expressly to test sewage sludge and results using these tests were compared with results from tests presently used to regulate ocean dumping of sewage sludges. Similar results were obtained in an interlaboratory comparison of methods using the same sludge samples from three wastewater treatment plants. It is concluded that the present, easier to conduct methods may be satisfactory to characterize acute toxicity of sludge.