To examine whether HSV, VZV, H. pylori and Candida that are known to be microorganisms causing ulcerative disease in oral cavity and have the relatively high contigiousness are detected in saliva of patients with RAU and related to the development with RAU, PCR and culture were performed on the saliva of 29 patients with RAU and 29 control subjects who visited the Department of Oral Medicine, Dental Hospital, Chosun University. The results were obtained as follows; 1. HSV DNA was detected in 41.4% patients with RAU, and 55.2% control subjects, however, a significant difference between the two groups was not detected, (P>0.05), and VZV DNA was not detected in both groups. 2. H. pylori DNA was detected in 27.6% patients with RAU, and 48.3% control subjects, however, a significant difference between the two groups was not detected (P>0.05). 3. Candida was cultured in 13.8% patients with RAU, and 6.9% control subjects, however, a significant difference between the two groups was not detected (P>0.05). This results suggest that HSV, VZV, H. pylori and Candida can not be regarded to play a direct role in the development of RAU. Thus it is considered that in future, on a larger sample, also, it has to be examined whether other microorganisms acts as a trigger factor of the development of RAU.