We used the computerized Moorfield Vision System to demonstrate specific increases in various perceptual visual thresholds in idiopathic Parkinson's syndrome. Fifteen patients were compared to 13 age-matched normals. Motion detection was impaired maximally (2 p < 0.01 and better in two-tailed t test) at luminance contrasts of 3-7%. Stimulus was an achromatic vertical 4 cycles/degrees sine wave grating subtending 3 degrees x 2 degrees, centered 5 degrees in the nasal field and oscillating at 5 Hz. In addition, stationary color and luminance contrast thresholds were tested with flashed display of 5 degrees x 6 degrees random letters, which were presented for 200 ms (color) and 50 ms (achromatic). Color discrimination was impaired in the tritan axis only (2 p < 0.05 in two-tailed t test). All achromatic stimuli--luminance increments, decrements, and phase reversing stimuli--were equally well seen by patients and controls. We conclude that the dopaminergic deficit of retinal amacrine cells in Parkinson patients can be monitored by combined low-contrast and motion (displacement) stimuli. Future studies will determine if moving colored targets are more effective in discriminating patients from controls than are the achromatic gratings used in this work.