The relationship between external reinforcement of behavior and depression is explored. Specifically, the psychological study measures the role of cognition in depression by comparing decision-making problems, lack of assertiveness, and perceptions of control in male and female undergraduate college students and psychiatric patients. It was hypothesized that the expectancy of external control would be associated with decision-making difficulty, choice inconsistency, depression, and lack of assertiveness. Procedure included administering decision-making and choice inconsistency tests to a sample of 102 college students and measures of depression and lack of assertiveness to additional samples of college students and psychiatric patients. Results indicated that externality was consistently and, often, significantly correlated in the predicted direction with decision-making, depression, and assertiveness. However, this relationship seemed to vary in intensity across sex and situation. Thus, it was concluded that externality in males is associated with decision-making difficulty and choice inconsistency, while externality in females is more closely associated with depression and lack of assertiveness. Implications of these data for the treatment of externally controlled clients through cognitive restructuring and training of specific behavioral skills are discussed. (Author/DB)