The paper presents two experiments which test the "change in feelings of competence and self-determination" proposition of cognitive evaluation theory. This proposition states that when a person receives feedback about his performance on an intrinsically motivated activity this information will affect his sense of competence and self-determination, thereby affecting his intrinsic motivation. Results of the experiments, performed with undergraduate students, indicate that positive verbal reinforcements decreased intrinsic motivation for females while they increased it for males, and that negative feedback decreased intrinsic motivation presumably by weakening the subject's feelings of competence and self-determination. These data, as well as other related studies, suggest that the traditional widespread use of external rewards and controls has had unintended, negative consequences on motivation and performance. This implies that we should begin to consider intrinsic motivation more carefully and structure reward and control systems which will be less likely to interfere with intrinsic motivation. (Author/SES)