Follicular lymphoma (FL) is pathologically categorised as a low-grade B-cell lymphoma and histopathologically shows follicular proliferation of neoplastic B cells. In the neoplastic follicles of FL, the presence of T cells, macrophages and follicular dendritic cells (FDCs) suggests that these cells may promote a favourable environment for the growth of FL cells. Because FL cells are generally associated with FDCs, FDCs may be considered an important source of cytokines and chemokines. FDCs form the framework for germinal centres and also provide networks for nodules of FL. To evaluate the gene expression in neoplastic follicles of FL and reactive follicles of reactive follicular hyperplasia (RFH), we performed gene expression profiling of FL (n=5) and RFH (n=5) using complementary DNA (cDNA) microarray of cytokines/chemokines and their receptors. FL and RFH exhibited a diffuse down-regulated profile compared with normal peripheral blood cells, which were used as controls, although some genes displayed up-regulated profiles. Hierarchical clustering analysis separated FL and RFH into two distinct groups based on their gene expression profiles. FL cases exhibited significantly higher expression of interleukin 3 receptor alpha (IL-3Ralpha) than RFH. Immunohistochemically, neoplastic follicles of FL frequently expressed IL-3Ralpha, especially in FDCs, but not in FL cells. However, IL-3Ralpha expression was rare or weak in the reactive follicles of RFH. These findings suggest the importance of the micro-environment for FL cell growth. Further studies of cDNA microarray should provide new insight into the molecular pathology of FL and may allow the design of improved therapies.