We studied the role of interleukin-1 beta (IL-1 beta) and basic fibroblast growth factor (bFGF) in the proliferative response of transformed human renal interstitial fibroblast cell lines established from either a kidney with glomerulonephritis and interstitial fibrosis or a normal kidney in comparison to primary human foreskin fibroblasts. Growth of fibrosis-derived renal fibroblasts was inhibited in the presence of IL-1 receptor antagonist (IL-1Ra) by 35% (P < 0.005), suggesting that these cells produce IL-1 and possess IL-1 receptors as part of paracrine growth. In contrast, spontaneous proliferation of fibroblasts derived from a normal kidney or normal skin were not inhibited by IL-1Ra. In fibrosis-derived but not in normal renal cells, fibronectin synthesis was increased 2.2-fold (P < 0.01) in the presence of IL-1Ra. Addition of exogenous IL-1 beta or bFGF stimulated proliferation of skin fibroblasts. In contrast, growth of fibrosis-derived renal fibroblasts was stimulated by IL-1 beta and unchanged by bFGF. Growth of normal kidney fibroblasts was unaffected by bFGF and inhibited by IL-1 beta. We conclude that compared to normal fibroblasts, fibrosis-derived renal fibroblasts have a different cytokine-response profile, are IL-1-dependent, produce IL-1 as a paracrine growth factor and do not proliferate to bFGF, a classical fibroblast growth factor.