Effect of quantity and nutritional quality of dietary proteins on the content of mRNA of insulin-like growth factor-binding protein-1 (IGFBP-1) was studied in rat liver and kidney. IGFBP-1 mRNA content per unit RNA increased in liver and kidney of rats fed on a protein-free diet and in those of fasted rats compared with that in the rats fed on a casein diet. When rats were given a gluten diet for 7 d, IGFBP-1 mRNA content in liver did not change significantly but that in kidney increased considerably compared with that in those organs of the rats fed on the casein diet. Because IGFBP-1 mRNA has been demonstrated both in liver parenchymal and non-parenchymal cells (Takenaka et al. 1991), the effect of the protein-free diet on these two types of cells has been studied. An increase in IGFBP-1 mRNA content under protein deprivation was observed in both liver parenchymal and non-parenchymal cells, suggesting that these two types of cells are regulated in a similar mode as far as IGFBP-1 mRNA content is concerned. The physiological and nutritional significance of the previously stated results on protein anabolism are discussed when considered together with our previous observations on the plasma concentrations of IGF-1 (Takahashi et al. 1990) and IGFBP (Umezawa et al. 1991) and insulin-like growth factor-1 mRNA content in liver (Miura et al. 1991).