Operating experiences and cost data gathered from site visits of eight, full scale, operating in-vessel sewage sludge composting facilities was summarized. The facilities visited represented the six in-vessel equipment suppliers who had full scale, operating plants in the U.S. at the time: American Bio Tech at Schenectady, NY; Ashbrook-Simon-Hartley at Newberg, OR; Fairfield (through Compost Systems Co.) at Plattsburgh, NY; Paygro (through Compost Systems Co.) at Akron, OH; Purac Engineering at Cape May County, NJ and Sarasota, FL; and Taulman-Weiss at Clayton County, GA and Portland, OR. Examples of both large and small plants were visited for Purac and Taulman-Weiss. As might be expected for any new, large scale, mechanically complex technology, these facilities had some operational problems. Odor problems in particular were more difficult to predict and control than anticipated during design. Difficulty with materials handling systems was the other major problem, but was being overcome on a site-by-site basis. The compost being produced at all of the plants surveyed had been approved by state agencies for public use except for application on food crops.