The present investigation is based on the cytomorphological, histopathological (HE, VG, PAS-Alcian, Safranin 0, Gömöri), histoenzymological (acid phosphatase, chondroitinsulphatase, peroxidase) and immunological (rheumatoid factor (RF), circulating immune complexes (CIC), anticolagen II antibodies and C reactive protein (CRP) study on ankylosing spondylarthritis (2.5 cases). The synovial fluid (SF) synoviocytogram showed cytosis (6.067/mm3), with polynucleosis (65.19%) and ragocytosis (17.73%) as compared with the hydrarthrosie SF characterized by lymphocytosis (47%). Enzymological findings revealed phosphatasic and myeloperoxidasic activity in the ragocytary polymorphonuclear (PMNs) and mononuclear cells. Histopathologically, the severe forms of AS correlated with villous chronic synovitis, associated to processes of obliterating vascularitis, fibrosclerosis, necrosis and calcification of disintegrated synovial structures. The articular cartilage was severly damaged, while osseous necrobiosis was noted at the osteocartilaginous junction. Histoenzymologically, the chondrocytes and synovial macrophages showed lysosomal and oxidative enzymatic activity. Immunological assessments (72 sera and 25 synovial fluid samples) showed pathological values of circulating immune complexes, anticollagen antibodies and C reactive protein. Correlation of immunocytomorphological findings demonstrates the involvement of immunologic and enzymatic factors in the pathogenesis of AS.