This study presents the clinical and laboratory findings of a novel syndrome associated with eosinophilia. Two young women presented with marked eosinophilia, and large, non-tender compressible articular nodules arising from the tenosynovium of extensor tendons, dermatitis, episodic swelling of the hands and/or feet and pain in adjacent muscles and joints. Tissue specimens were examined by routine haematoxylin and eosin staining, immunofluorescent staining for eosinophil granule major basic protein (MBP) and rhodamine-avidin or tryptase staining for mast cells. Plasma levels of MBP and eosinophii-derived neurotoxin (EDN) were quantilated by immunoassay. The first patient presented in 1967 at the age of 20 and had, in addition to nodules and eosinophilia, dermographism, recurrent episcleritis and axillary urticaria. Biopsy of a nodule showed lenosynovitis with necrotizing granulomas, non-specific vasculitis, eosinophils and eosinophil degranulation as shown by extracellular deposition of eosinophil granule MBP. Her symptoms responded to low-dose, alternate-day predni-sone and have remained quiescent over the past 15 yr. The second patient presented in 1990 at the age of 28 with generalized pruritic dermatitis for 15 yr, eosinophilia for 2 yr. subcutaneous nodules and non-limiting pain in several joints. Biopsy of a nodule showed chronic mild tenosynovitis, numerous eosinophils and extracellular deposition of M BP. She remains untreated. Serum IgE values and plasma levels of M BP and EDN were elevated in both patients; mast cells were numerous in their synovial tissue. Based on their clinical courses, these patients reveal the existence of a distinctive, relatively benign eosinophilic disorder with good long-term prognosis.