The report represents an interim protocol for performing research to measure microbial degradation rates of organic chemicals in freshwaters. For chemicals, a major transformation pathway influencing their environmental fate is microbial degradation. The interim protocol presented provides a basis for measurement of microbial degradation rates such that reliable, comparable and consistent data can be obtained by different laboratories and investigators. As additional research and information is gathered on the environmental factors affecting microbial degradation by suspended bacterial populations in freshwaters, the outlined protocol will be modified.