Tolonium chloride (toluidine blue) application is useful for identifying malignant changes in squamous mucosa. However, early asymptomatic mucosal changes may remain undetected by tolonium application. A study was carried out to determine the feasibility of using a tolonium mouth rinse as a routine procedure after thorough clinical examination, to discover undetected cancers. A proved, effective tolonium application method was compared with a rinse sequence. One hundred five asymptomatic oral lesions (51 carcinomas and 54 nonmalignant lesions) that persisted for ten to 14 days were evaluated with application and rinse modalities and biopsies. There were 2% false-negatives (1/51) with the application as opposed to 5.9% (3/51) with the rinse and 9.3% false-positives (5/54) with the application as compared to 7.4% (4/54) with the rinse. Four inapparent, second primary cancers, unobserved for application, were delineated by the rinse (three oral, one pharyngeal). Tolonium blue rinse may be used to detect unobserved, asymptomatic oral mucosal cancers after clinical examination. After a positive rinse stain, a subsequent positive application stain ten to 14 days later mandates a biopsy of the lesion.