Research was conducted to develop operating techniques and define some of the limiting parameters for microbially converting hydrous calcium sulfate to hydrogen sulfide. The work was carried out in either glass stoppered flasks or anaerobic fermentors. Using the criteria of ph, temperature, number of bacteria per milliliter of test solution, and hydrogen sulfide produced, it was shown that hydrous calcium sulfate could be microbially converted to hydrogen sulfide at a rate of 7.3 G h2s/l of fermentor volume per 24 hours. The various parameters defined were ph, temperature, and medium exchange rate. These were shown to be a ph range of 7.2 to 8.8, A temperature range of 30 deg. to 35 deg. C, and a medium exchange rate of 70 percent of the fermentor volume per 24 hours. It was also shown that a daily waste was between 50 and 77 percent as effective as sodium lactate in supporting the production of hydrogen sulfide and that by utilizing a gas to purge the fermentation system, a 1.7-Fold increase in hydrogen sulfide was obtained.