While early work on money demand estimation focused primarily on the importance of domestic variables, many studies in later years have suggested that foreign variables also influence the domestic demand for money in an open economy. With the rapid financial market liberalization in some of the Asian economies in the last couple of decades, open economy factors have become very important in the determination of money demand. Therefore, this paper aims to ascertain the degree to which foreign opportunity cost variables influence money demand in the Philippines, Singapore and South Korea. Cointegration analysis is performed and an error correction model estimated using quarterly time-series data. The empirical results support the inclusion of foreign opportunity cost variables in the money demand function.