An analysis of measurement variability associated with determining upper extremity postures in video display terminal (VDT) operators was performed. Ulnar deviation, wrist extension, shoulder flexion, shoulder abduction, elbow angle and the gaze angle were measured on 19 VDT operators, 17 females, mean age 38.8 years, by two raters using manual goniometry. The measurements were made on six occasions: Monday, Wednesday, and Friday mornings and afternoons. The two raters were professional ergonomists experienced with measuring postures in the field who were blind to each other's measurements. Between subject and within subject variances were computed from the data and compared using an analysis of variance procedure. The overall means and their standard deviations for ulnar deviation, wrist extension, shoulder flexion, shoulder abduction, elbow angle, and gaze angle were 8.8+/-7.2, 31.2+/-13.9, 17.4+/- 12.1, 16.0+/-7.2, 105.0+/-11.6, and 8.9+/-6.8 degrees, respectively. Between subject variability was significantly larger than within subject variability for each postural angle. The mean angles measured for ulnar deviation, wrist extension, shoulder flexion, elbow angle, and gaze angle were similar to those measured previously by NIOSH in a study of communications workers using VDTs. No significant main effect for day of the week for any postural angle occurred. Time of day was significantly associated with mean gaze angle, the angle observed in the morning being slightly smaller than in the afternoon. No significant main time of day effect was seen for the other postural angles. The authors conclude that manual goniometry can provide information about upper extremity postures among VDT users that is useful for epidemiologic studies of upper extremity musculoskeletal disorders.