Non specific inflammations of the intestine are the group of chronic disorders, such as ulcerative colitis and Crohn's disease and with episodic aggravation of inflammatory lesions, called active phase and non-active phase, called remission. Non-steroid antiinflammatory drugs (NSAIDS) are one of the most frequently used medications in the World. NSAIDS therapy in ulcerative colitis patients is a very important clinical problem, because of frequent extraintestinal symptoms, such as arthritis, which make patients to take these drugs. But the mechanisms of the NSAIDS influence on the course of inflammatory diseases of inferior part of gastrointestinal tract is still not known. Our results of clinical studies indicated the influence of nonselective and selective COX2 inhibitors on ulcerative colitis activity. However clinical aggravation was detected in 8% of patients treated with conventional NSAIDS and in one person administered selective COX2 inhibitor. Administration of the conventional NSAIDS as well as coxibs, significantly influenced severity of diarrhea. Moreover conventional COX inhibitors increased severity of colon bleeding and endoscopic colon inflammatory lesions in comparison to ulcerative colitis patients, as well not administered NSAIDS as given coxibs. Total patients evaluation involving the intensity of clinical symptoms did not reveal significant differences between examined groups. The above results showed, that the balance between risk and advantages resulting from administration of NSAIDS both, non-selective and selective COX is to be accepted in ulcerative colitis patients in non-active phase.