In an open, controlled study we treated 55 patients suffering of psoriatic arthritis (PsA), 29 patients suffering of Bechterew's disease (MB) and 16 patients with Reiter's syndrome with Salazopyrin at a daily dosage of 2000 mg. We monitored the following criteria of activity: duration of morning stiffness, joint index, global well being scored by the patient and erythrocyte sedimentation rate. All these criteria improved during the treatment; there was a profound improvement in the RS group, whereas the MB group showed only a slight improvement; the PsA group ended between this two extremes. The effect of the drug appeared between week 5 and 15 of treatment. 21% of all patients had to discontinue the treatment because of severe side effects; this figure correlates with the percentages given in the literature. Most of these side effects appeared from week 3 to week 7 of treatment; after week 15 none of the patients had to discontinue the medication of because of severe side effects.