Granulocyte colony-stimulating factor (G-CSF) is the cytokine that is critical for polymorphonuclear neutrophilic granulocyte (PMN) production as well as being a potent agonist of PMN activation. We have recently re ported that in the lung and the liver of rats resuscitated after hemorrhagic shock (HS) G-CSF mRNA expression is induced. It is not known if both phases of HS, the ischemic and the reperfusion phase, are required for G-CSF mRNA induction. The present study was designed to test the hypothesis that the upregulation of G-CSF mRNA expression is the consequence of HS followed by resuscitation and that ischemia alone is insufficient to induce G-CSF mRNA expression in the affected organs. Male Sprague-Dawley rats were subjected to resuscitated and unresuscitated shock protocols of varying severity. Control animals were subjected to anesthesia and all surgical preparations except for hemorrhage. Lungs and livers were isolated and their RNA extracted. Using semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR), we demonstrated that G-CSF mRNA was induced in the lung and liver of shock animals above the level observed in control animals. Upregulation of G-CSF mRNA relative to controls occurred only in animals undergoing resuscitated HS and not in ones subjected to unresuscitated HS. These results indicate that G-CSF production specific for the hemorrhage component of shock is dependent on resuscitation. As a consequence, the production of this cytokine may be decreased through modifications in the resuscitation protocols.