141 patients with seronegative spondylarthritis including ankylosing spondylarthritis (n = 90), reactive arthritis and Reiter's disease (n = 51) took water radon baths (concentration 1.5, 3.0 and 4.5 kB/l). The baths proved similarly effective in patients with seronegative spondylarthritis. They produced analgetic, anti-inflammatory actions, raised quality of life for such patients.