&NA;In 28 patients who had previously had a proctocolectomy for ulcerative colitis, the ileostomy output of feces was determined before and after conversion to continent reservoir ileostomy, as was the output of gas in 20 of the patients. The median output of feces/24 hours collected in the hospital was 576 g before and 692 g after conversion(P< 0.05); when collected at home the corresponding figures were 734 g and 740 g, respectively. In the majority of patients, the change in fecal ileostomy output after the conversion was not considerable, while in a few patients there was a marked increase. The fecal output was 24 percent(P< 0.01) and 11 percent(P< 0.01) larger at home than in hospital before and after conversion, respectively. The proportion dry weight of ileostomy discharge decreased after conversion(P< 0.01). The median gas volume in the ileostomy output/24 hours was 1,664 ml before and 1,450 ml after conversion. The gas constituted 58 percent of the output and is significant with respect to the required reservoir capacity. Recording the emptying volumes and frequency in patients with reservoir ileostomy showed that, in general, patients with large output expand their reservoir capacity instead of increasing their emptying frequency.