Solid solutions between zinc oxide and magnesium oxide containing up to 4 at.% Mg were grown from the melt using a modified Bridgman technique. Chemical analysis (ICP-OES) and photoluminescence (PL) measurements revealed that the Mg concentration in the melt is larger compared with the starting material. This observation contradicts the commonly accepted assumption, that the ZnO-MgO phase diagram is of eutectic type. Peritectic melting of Zn-rich Zn1-xMgxO can explain the new experimental results, and a new ZnO-MgO phase diagram is proposed. Furthermore a distribution coefficient for Mg of k(eff) = 1.32 ... 1.4 has been determined. (C) 2011 Elsevier B.V. All rights reserved.