Methyl mercury is a global pollutant of great environmental concern. The methylation of inorganic mercury to form methyl mercury is a process known to be performed by a number of bacteria. This project was intended to survey a number of bacteria for; cobalamin content, ability to methylate mercury, and to investigate molybdate as a microbial inhibitor, and in particular its mode of action on SRB. For species testing positive for the ability to methylate mercury, further investigations were conducted to examine physical factors affecting methylation activity. These factors were, low total mercury content, pH, substrate composition, temperature, gas phase, and nickel concentration. Of the organisms surveyed for mercury methylation, some of which have been shown by other workers to methylate mercury, only two SRB species were capable of methylation. (Abstract shortened by UMI.)