Objective: To present a practical and technically simple method for clinical diagnosis of oral melanomas that allows to differentiate this neoplasm from other pigmented lesions. Patients and methods: Thirteen oral pigmented lesions with suspected diagnosis of mucosal melanomas were submitted to a test named "rubbing with a gauze" the surface of the lesion. The test was considered positive when the gauze stained dark brown or black due to the presence of melanin-laden cells on the epithelial surface. In all cases definite diagnosis was confirmed by biopsy. Results: Positive results were obtained in 11 out of 13 cases (84.6%). Conclusion: Our results establish that the test "rubbing with gauze" the surface of oral pigmented lesions demonstrates a high sensitivity to anticipate clinically the diagnosis of mucosal melanomas. However, a negative result does not exclude this neoplasm, since there are some cases in which malignant cells have not invaded the superficial epithelial layers. In every case the final diagnosis must be established by histopathologic or immunohistochemical analysis.