Anaerobic waste treatment is a biological process. As such it depends for successful operation on the maintenance of a proper environment for the organisms involved. By delineating this proper environment, a more complete understanding of the process will be attained. This will lead to an increase in the operational control and predictability of anaerobic treatment. Special attention must be focused on the problem of toxicity-causing substances if anaerobic treatment, long a mainstay of municipal sewage treatment, is to be successfully extended to the treatment of complex industrial wastes. The effects of high sulfide concentrations on anaerobic treatment are not well understood, and were explored in this investigation.