There are few 'second-line' drugs available for the treatment of immunological disturbances in psoriatic arthritis (PsA) and their use is often limited by nonspecific activity and toxicity. Viusid is accepted as an effective immunomodulator drug for treating different immunodeficiency diseases, but rarely evaluated in psoriatic arthritis. An earlier open study suggested that it was well tolerated and potentially beneficial. The present study of 17 patients has now confirmed its efficacy as immunomodulator in PsA immunological disturbances patients with active PsA recruited from Rheumatology department of Republican Clinical Hospital, they have administrated Viusid 9,0 gr per day 2 months (group 1). Eight patients with active PsA have been treated without Viusid (group 2). In both groups we have studied immunological status (cellular and humoral). Evaluation of effect of treatment revealed significant improvements in immunological indexes in group with Viusid. By 4 wk the immunocellular indexes in that group was still showing benefit. Greater improvement occurred in those patients on active treatment by 6 wk, with more benefit being detected in immunohumoral status (normalization of Ig G, M, A and circulatory immunocomplexes) which were associated at the beginning with a high acute-phase response. No exacerbation of psoriasis was observed in first 6 months. This study is in progress now to determine the degree of efficacy of Viusid in different clinical subgroups of psoriatic arthritis. In addition to immunological index the Viusid group improved significantly in terms of visual analogue scale, duration of morning stiffness. Viusid is effective in immunocompetent control of PsA and indicates the importance of such studies in this variable disease.