Reiter's syndrome is usually a benign disease of a rather short duration, but in some patients it can take a lingering or chronic form. The clinical picture of a chronic Reiter's syndrome can be severe with chronic iridocyclitis, joint destruction and spondylitis. These patients constitute a considerable therapeutic problem.The aim of this study was to evaluate the duration of the active phase of Reiter's syndrome and to characterize patients with a lingering or chronic form of the disease.The patient sample consisted of ISO patients with Reiter's syndrome investigated at the Institute of Rheumatology, Moscow. A total of 116 had a urogenital and 34 patients an entero-colitic form of the disease. The aetiology of the triggering infection was studied by routine microbiological and serological methods. Yersinia enterocolitica infection was found in 9 patients, and chlamydia antibodies in 112 patients.In 108 patients (72 %), the duration of the active phase of the disease was less than 6 months, in 26 patient...