The semen qualities of six patients with salicylazosulfapyridine-treated chronic ulcerative colitis are discussed. Over-all poor parameters were observed during the treatment period. Reduced motility and a shift in morphology were the most significant abnormalities in the specimens. A characteristic megalo cell type occurred in the morphology with a frequency of 3% to 8%. In three patients when no medical contraindication existed, discontinuation of the drug resulted in a dramatic improvement in the semen quality, and all three reported pregnancies within the ensuing 3 months. A possible reversible toxic effect of salicylazosulfapyridine on semen quality is discussed.