The experiments described in this report were part of a sediment bioassessment study involving several laboratories. The concept behind the study was to compare the bioassessment results of each participating laboratory, each using whatever assessment technique they currently employed, on two common sediment samples from Toronto and Toledo harbors. Our first experience with these bioassay methods indicated that when comparing the toxicity of an array of variably contaminated sediments, they yield qualitatively similar results, although relative quantitative sensitivity between test procedures can vary from time to time. Generally, the Daphnia are the most sensitive of our test organisms and their response generally follows the solubilization of the toxic chemicals from the sediments. This solubilization varies among the three test types and their effective sediment: water ratios. Above all, solubilization (and loss from solution) is a dynamic process and proceeds at different rates depending on test and sediment type as well as organism activity.