Perceptions of supervisor bias can profoundly affect organizational climate and employees' morale. Based on attribution theory, it was predicted that bias would be used to explain denial of promotion when the employee had been expected to succeed. It was also predicted that social comparison information detailing the similar plight of peer women or the good fortune of peer men would enhance attributions of sexism. College students (N=60) read the career histories of women who had been denied promotion by their male bosses. Expectations of success were manipulated by presenting information that indicated level of ability and quality of the employee's past performance. Participants explained the denial of promotion by rating the employee's ability and effort, the difficulty of her job, and the supervisor's sexism and incompetence. Results supported predictions. Magnitude of attributed sexism was greater when the employee was described as having both high ability and an excellent record of past performance. Both information concerning the similar plight of peer women and the good fortune of peer men increased the magnitude of attributed sexism. Further support for an attributional model of bias was obtained from ratings of employees' effort and job difficulty. Limitations of the generality of the findings are discussed, and references are include, along with three data analysis graphs. (Author/TE)