Contrast sensitivity responses were determined in diabetic subjects with retinopathy, macular disease and cataract. The test proved reliable in discriminating between different degrees of cataract and between diabetics with no retinopathy, mild background retinopathy and early maculopathy. Background retinopathy was shown to produce a loss of contrast sensitivity particularly at the low and medium frequencies. These thresholds increased with macular involvement. Mild cataract was correlated with loss at the low and medium spatial frequencies, whilst moderate cataract suppressed sensitivity to all frequencies. Results are compared to colour discrimination in each patient.