Polyamine metabolism in mucosa both from patients in the active or remission stage of ulcerative colitis (UC) and from healthy controls was studied. In the active stage of UC, mucosal spermidine concentration was higher than in remission or in the controls, but the activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase, rate-limiting enzymes of polyamine biosynthesis, were lower. In the active stage of UC, the mucosal level of mRNA coding for ornithine decarboxylase was lower than in the remission stage of UC or in the controls. The activity of spermidine/spermine N1-acetyltransferase, the rate-limiting enzyme of polyamine degradation, was higher in the active stage of UC than in the remission stage of UC or in the controls. However, it seemed that this activity did not reflect the increase in the spermidine concentration. The results showed that the spermidine increase in the active stage of UC was not due to changes in the synthesis or degradation of polyamines; the increase may have been due to increased exogenous spermidine uptake.