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We have partially purified and characterized two protein kinases that were strongly activated by interleukin-1 (IL-1) or tumor necrosis factor (TNF) in MRC-5 fibroblasts. The kinases were separated by anion exchange chromatography of cytosolic fractions. They phosphorylated in vitro the small heat shock protein (hsp27) or beta-casein and were stimulated 3- and 4.5-fold, respectively, in cells that had been exposed to IL-1 or TNF for 10 min. They were distinct from the mitogen-activated protein kinases, whose activation by IL-1 or TNF has been reported recently. The hsp27 kinase phosphorylated its substrate on serine residues. Its molecular mass was estimated to be 45-kDa by gel filtration. It is probably involved in the increase in hsp27 phosphorylation seen in intact cells. The beta-casein kinase behaved as a 65-kDa protein. It phosphorylated its substrate on serine and threonine residues and had little activity on alpha-casein. The hsp27 and beta-casein kinases were not activated after stimulation of the cells with phorbol myristate acetate (PMA). In contrast, the MAP kinases were activated to a similar extent (2-3-fold) by the cytokines and by PMA. The hsp27- and beta-casein kinases probably correspond to novel enzymes whose mechanisms of activation may be independent of protein kinase C or MAP kinases.