The solubility of cerium-monazite (CePO4) in SiO2-Al2O3-K2O-Na2O melts was determined at 800 °C, 2 kbar, under water-saturated conditions. Dissolution experiments using synthetic Ce-monazite crystals and crystallization experiments using Ce and PO4-bearing glasses yield results in good agreement. Microprobe analyses of glasses using a sensitive method (detection limit to <130 ppm) show that the solubility of monazite is dependent on the melt composition and is especially low for peraluminous compositions. Application of these data to various geologic occurrences is in good agreement with petrographic and geochemical observations and shows that monazite fractionation is probably a very common phenomenon in two-mica granites. This provides a good explanation for the light REE and Th depletion commonly observed in such rocks.