The ability of dimethyl sulfoxide (DMSO) to induce the acute-phase (AP) response was examined. Injection of DMSO to laboratory rats caused a rapid doubling of the plasma corticosterone concentration 2 h after treatment. The elevated corticosterone concentration promoted the synthesis of mRNAs for several AP reactants. At 24 h after DMSO administration the relative serum concentration of cysteine-proteinase inhibitor (CPI) increased about 710%, alpha1-acid glycoprotein (AGP) 630%, alpha1-macroglobulin (MG) 510%, gamma fibrinogen (Fb) 420%, haptoglobin (Hp) 280%, whereas the relative concentration of albumin, a "negative" AP reactant, decreased to 93%. The extent and kinetics of the corticosterone increase and the general increase of AP reactant mRNAs and protein serum concentrations after DMSO administration corresponded to the overall changes observed during the turpentine-induced AP response. On the basis of these findings it was concluded that DMSO was capable of promoting the AP response in rats.