The purpose of this study was to compare multiple indicators of behavior and identify the most viable measure of blue-collar workers 'use of hearing protection. Three measures of use were employed: observations, supervisor report, and self-report. Supervisor report was highly discrepant from both self-report and observed use; self-report and observations were highly correlated, and discrepancies between the two were slight. These results suggest that, for this type of measurement, self-report is an appropriate measure and may be the best choice when time and monetary resources restrict measurement to one indicator