High-temperature solutions of the systems K2W2O7-KGd1-xLnx(WO4)2 (x=0.05, 0.10, 0.20 and 0.50; Ln=Er, Eu and Ho) were investigated. The solubility curves were plotted for each x value and each dopant and the concentration and temperature regions of crystallization of the low-temperature monoclinic phase were determined. The distribution coefficients were determined for gadolinium and for the dopants. The data obtained were compared with the distribution coefficients in the case of double doping of KGd(WO4)2 with erbium and neodymium.