The effects of a myeloablative sublethal 775 cGy 60C gamma radiation exposure on endogenous bone marrow (BM) and splenic granulocyte-macrophage colony-stimulating factor (GM-CSF) and transforming growth factor-beta (TGF-beta) mRNA levels were assayed in B6D2F1 female mice. BM and spleen were harvested from normal mice and irradiated mice on days 2, 4, 7, 10, and 14 after exposure. Cytokine mRNA levels were determined using reverse transcription-polymerase chain reaction. After irradiation, GM-CSF mRNA levels were significantly increased in the BM from days 2 to 10 and in the spleen from days 4 to 10. However, when BM and splenic GM-CSF protein levels were measured using Western dot blot, no increased protein levels were detected. Serum GM-CSF levels were likewise unchanged. Radiation exposure did not affect BM or splenic TGF-beta mRNA levels and this cytokine is known to be produced by cell populations similar to those that produce GM-CSF. These data suggest that radiation injury to hemopoietic tissues results in differential effects on GM-CSF and TGF-beta mRNA levels and that, in the case of GM-CSF, increased mRNA levels are not matched by increased protein production.