Sulfasalazine is of proven therapeutic value in chronic inflammatory bowel diseases (ulcerative colitis and Crohn's disease in the colon) of mild and moderate degrees. However, owing to adverse effects (allergy, dyspepsia), this drug often has to be withdrawn. The present work analyzes, in 704 patients with chronic inflammatory bowel disease, the frequency of such side effects that over a 15-year period necessitated withdrawal of sulfasalazine (Salazopyrin). A total of 17% of the patients developed dyspeptic manifestations, whereas extraintestinal manifestations, mainly exanthema and fever, occurred in 13%. Out of 121 patients with dyspeptic troubles, 107 had Salazopyrin replaced by EN Salazopyrin (dragées), and in 102 of them dyspepsia did not recur. Salazosulfadimidine (Azudimidine) was given to 48 patients who had developed extraintestinal manifestations when receiving sulfasalazine. Only 29% of these patients developed intolerance to this drug too. Generally, dyspepsia occurred within the first days after institution of treatment, extraintestinal manifestations after 1 to 3 weeks.