A study of absolute basophil counts and plasma levels of highly sulphated glycosaminoglycans in 30 peripheral blood samples from 21 patients with different leukaemias was performed. This revealed significantly raised levels of both plasma highly sulphated glycosaminoglycans and basophils in those patients with chronic myeloid leukaemia, as compared to those with other types of leukaemia and 35 normal controls. A strong correlation (r = 0.83) was observed between the levels of highly sulphated glycosaminoglycans and basophil counts in the group as a whole, supporting a direct relationship between the two. The elevated plasma levels of highly sulphated glycosaminoglycans may contribute to the bleeding tendency reported in some patients with chronic myeloid leukaemia.