In 58 patients with mast cell disease (MCD) and three with basophilic leukemia, bone marrow (54 cases) or skin tissue (four cases) was studied immunohistochemically for expression of Kit (c-kit protein), the different isomers of transforming growth factor-beta (TGF-beta), basic fibroblast growth factor (bFGF), and their respective receptors. Kit was expressed in all cases of MCD but in none of basophilic leukemia. Expression pattern of cytokines and their receptors was variable in systemic MCD with (SMCD-HD) or without (SMCD) associated hematologic disorder. However, type I TGF-beta receptor (TGFbeta1R) was not expressed in 30% of SMCD-HD patients or in patients with mast cell leukemia, but the remaining cases of MCD showed near uniform expression. The associated hematologic disorders in TGFbeta1R-negative cases of SMCD-HD were prognostically less favorable than those associated with TGFbeta1R-positive cases of SMCD-HD. The results confirm the diagnostic value of Kit immunohistochemistry in MCD and suggest a biologically relevant heterogeneity in TGFbeta1R expression among patients with SMCD-HD.