Abstract
Three hundred and twenty-one synovial fluids from the knees of patients with six different inflammatory arthropathies have been examined for the presence of cytophagocytic monocytes (CPM) and mast cells. Both cell types were seen independently in many of the fluids examined but were found together only in those patients with Reiter's disease, psoriatic arthritis, ankylosing spondylitis, and enteropathic arthritis. These four disease groups also contain the highest proportion of patients with mast cells in their synovial fluids and those individuals with the greatest number of synovial fluid CPM. Criteria have been developed from these observations which may be employed in the differential diagnosis of inflammatory arthropathies.