Immunoglobulin allotyping carried out on patients with ankylosing spondylitis, psoriatic arthritis and psoriasis alone showed increase in the phenotype G1m(1,2,3);G3m(5,11,21) in the psoriasis patients in general (p less than 0.05). In patients with psoriasis alone this increase was of greater significance (p less than 0.01). No significant deviation from the normal controls was found in ankylosing spondylitis.