Two cotton thread tests (a self-prepared cotton thread test (SP-CTT) and the Phenol Red Thread (PRT) test) were performed on 46 dry eye and 37 normal Hong Kong (HK)-Chinese, all subjects being diagnosed by ophthalmologists in a private clinic. The mean SP-CTT value for the dry eye subjects (mean +/- SD: 6.2 +/- 4.2 mm/15s) was significantly lower than that of the normal subjects (8.3 +/- 4.3 mm/15s). However, no significant difference in the mean PRT value was found between the two groups (dry eye subjects: 10.7 +/- 4.5 mm/15s; normal subjects; 11.4 +/- 4.5 mm/15s). The specificity and sensitivity of the SP-CTT were 78.4% and 45.7 when a cut-off value of < or = 4 mm was used, and 56.8% and 65.2% when the cut-off value was changed to < or = 6.5 mm. Our results showed that the specificities and sensitivities of both tests were poor when applied to these dry eye patients.