In a small bowl, beat the cream cheese, mustard and horseradish until blended. Spread a heaping tablespoonful of cream cheese mixture over each tortilla.
Layer each tortilla with eight slices of corned beef, three slices of cheese, another heaping tablespoonful of cream cheese mixture and 1/2 cup sauerkraut. Roll up tightly. Chill for 1 hour. Cut each roll-up into 1/2-in. slices. Yield: about 8 dozen.