The anticoagulant activity of proteoglycans released from human basophils was evaluated. Basophils were obtained from normal donors and patients with abnormally high peripheral blood basophilia accompanying chronic myelogenous leukemia (CML) and enriched by Hypaque-Ficoll gradient sedimentation. From normal donors (8.9±4.6)×10(6) basophils were obtained with a purity of 6.2±1.7%, and from patients with CML (1.4±0.3)×10(7) basophils were obtained with a purity of 52.1±6.9%. Isolated basophils from normal donors, which were passive-sensitized with high IgE serum from an allergic patient and challenged with rabbit anti-human IgE or stimulated by calcium ionophore A23187, released proteoglycans which stained metachromatically with Azure A, as well as histamine. No anticoagulant activity was detected in proteoglycans released from human basophils by the amidolytic method using chromogenic substrate S-2238. Isolated basophils from patients with CML, which were labeled by [(35)S] sulfate, were also passive-sensitized and challenged with rabbit anti-human IgE. Released [(35)S] proteoglycans filtered on Sephadex G-25 were resistant to heparinase and chondroitin-6-sulfatase, and susceptible to degaradation by chondroitin ABC lyase, chondroitin AC lyase and chondroitin-4-sulfatase. These findings indicate that the [(35)S] proteoglycans released from basophils were made up of chondroitin sulfate type A. No heparin was identified. The basophil proteoglycans had no anticoagulant activity and were different from the proteoglycans of human lung mast cells. This fact may be particularly relevant to the location of each cell.