Two studies investigating the effects of pay on the intrinsic motivation of subjects varying along the dimension of locus of control were conducted. It was hypothesized that internals, who should assign greater weight to the competency aspect of rewards they receive, would manifest increasing intrinsic motivation as pay increased. Externals, who should be more likely to focus on the controlling aspects of rewards, were expected to show decreases in intrinsic motivation as rewards increased. In Study 1, where both the controlling and competency aspects of the rewards offered were deliberately kept vague, the hypotheses were supported. In Study 2, where the controlling aspect of the pay offered was made salient by making pay contingent upon performance, high pay undermined the intrinsic motivation of both internals and externals. It was suggested that only when the controlling aspect of pay is not salient will the intrinsic motivation of externals and internals be differentially affected. Support for the hypothesis that internals and externals differentially weight available information when making causal attributions was also noted.