Master production scheduling is one of the most important activities in production and operations planning. Many firms utilize rolling schedules and master production schedule freezing methods as means to respond to demand changes under uncertainty and to reduce master production schedule instability. The decline in service levels resulting from freezing a portion of the master production schedule can be addressed through the use of safety stock. This study compared the case of holding safety stock only for finished goods versus simultaneously holding safety stock for both finished goods and components under a multi-echelon material requirements planning system. The results showed that total costs were minimized when the safety stock levels for both finished goods and components were maintained at levels equal to the standard deviation of forecast errors.