Effects of extrinsic rewards upon intrinsic motivation were investigated in a 2 x 2 X 2 (immediate/delayed reward x performance contingent f task contingent reward x high/low reward conditions) factorial experiment on 80 graduate students. Two performance measures, one measure of task interest and two measures of task involvement were used as dependent variables. Major findings of the study were that performance contingent rewards resulted in marginally better performance than task contingent rewards and greater involvement in the task, but not necessarily in greater perceived interest in the task. Delayed rewards resulted in better subsequent performance on intrinsically motivated task and greater perceived interest but not in greater involvement. High rewards did not have a significant influence on either subsequent performance of the intrinsically motivated task or on task involvement, but resulted in perception of significantly greater interest in the task as compared to immediate rewards. Several interaction effects were also found to be significant. Implications of findings have been discussed in the light of cognitive evaluation theory.