The adjuvant disease of the rat is an experimental disease, not only important as an arthritis model, but also as an "urethritis model" in clinical and therapeutical respects. The polyarthritic syndrome in rats following injection of Freund's adjuvant also shows regularly involvement of the genitourinary system. Urethritis, cavernitis, and balanitis are common inflammatory manifestations of the penis, which can mostly be observed. In the peritesticular and periepididymal fat, granulomata and nonspecific inflammatory reactions do occur. Prostata, bladder, kidneys, testes, and epididymis are seldom involved in the inflammatory process. This therapeutical study demonstrated clearly that acetylsalicylic acid (dosage: 80 mg/kg BW/day) cannot be of benefit for these changes. However, it was possible to significantly influence the inflammatory changes by using prednisolone (dosage: 1.5 mg/kg BW/day).