Abstract: In a study on 391 cases of BD presented to the EULAR Congress in 1987 we demonstrated that the following symptoms were seen more frequently in patients with positive pathergy phenomenon: oral aphthosis as the initial manifestation of the disease, genital ulcerations, pseudofolliculitis, and arthralgia. The following symptoms, on the contrary were seen less frequently: oral aphthosis, ankylosing spondylitis. It was interesting to look after those findings, 6 years later, in a much more larger group of patients. For this purpose ?? patients were analyzed. We found the same results except for pseudofolliculitis. As the pathergy phenomenon seems to have the same characteristic of other manifestations of BD (waxing and waning) it was interesting to look at the manifestations of BD when the pathergy phenomenon was positive. For this study we analyzed 245 patients. Symptoms present at the day of pathergy test were compared in patients with positive and negative reaction by the chi square test. The confidence interval (CI) as calculated for the percentages. The positive group had 128 and the negative group 117 patients. Surprisingly we found other relationship between the pathergy phenomenon and BD manifestations. Oral aphthosis was present at the same time of positive pathergy test in 64.1 % of patients (CI = 8.3) while it was present only in 44.4 % of patients (CI = 9) when the pathergy was negative (x2 = 9.494, P = 0.002). Anterior uveitis was seen in 21.9% of patients in the presence of pathergy phenomenon (CI = 7.2) and in 40.2 % of patients (CI = 8.9) in its absence (x2 = 9.633, P < 0.002). The difference was not statistically significant for other manifestations. The above results seems to demonstrate that the mechanism which produces the pathergy phenomenon enhances oral aphthosis while it inhibits the anterior uveitis. The positive relationship of pathergy phenomenon and oral aphthosis does seem to be related to the genetic marker B5. On the contrary, the negative relationship of pathergy phenomenon and the anterior uveitis is seen only in patients with negative B5, but not in patients with positive B5 (x2 = 7.957, P < 0.005).