Previous investigations from our laboratory have shown that the benzene metabolite, hydroquinone (HQ), inhibits B cell production by preventing the maturation of pre-B cells. Data presented in this paper demonstrate that HQ interrupts B-lymphopoiesis indirectly by inhibiting the production of interleukin-4 (IL-4) by fibroblastic stromal cells. HQ exposure of fibroblastic stromal cells (SCL-173 and SCL-160) did not affect IL-4 production by these cell lines at any dose tested. Addition of untreated bone marrow-derived macrophages to HQ-treated bone marrow stromal cells (heterogeneous population of fibroblastic cells and macrophages) reversed inhibition of IL-4 production. However, addition of HQ-treated macrophages was without effect. Our studies suggest that HQ inhibits macrophage production of IL-1, a potent inducer of IL-4 production by bone marrow fibroblastic stromal cells. Interruption of IL-1 release from macrophages mediates the observed inhibition of B lineage cell maturation.