The undercooling behaviour and formation of metastable microstructures have been studied in the melt of Cu-Ag alloy entrained in its primary phase. A maximum undercooling of 180 degrees C below the liquidus temperature was observed in isolated liquid droplets. The highly undercooled droplets underwent a massive transformation which resulted in the formation of a metastable solid-solution phase containing Ag-28 at % Cu. The metastable phase decomposed on ageing to form the equilibrium phases. The undercooling behaviour and evolution of metastable microstructures in droplets are discussed.