The present study is a follow-up report on the use of bleeding on probing (BOP) as a clinical indicator for disease progression or periodontal stability, respectively. Following active periodontal therapy, 39 patients were incorporated in a program of supportive periodontal therapy for a period of 53 months with recall intervals varying between 2-8 months. The patients received supportive therapy 7 to 14 x. At the beginning of each maintenance visit, the tissues were evaluated using BOP. Reinstrumentation was only performed at sites which bled on probing. However, supragingival plaque and calculus were always removed. Probing depth and probing attachment levels were determined after active treatment and at the conclusion of the study. Progression of periodontal disease was defined by a measured loss of probing attachment of 2 mm or more. During the observation period, 4.2% of all the sites lost attachment. Approximately 50% of these losses were due to periodontal disease progression, while the other half was the result of attachment loss in conjunction with recession of the gingiva. 2/3 of all the sites which lost attachment were found in a group of patients which presented a mean BOP > or = 30%. In a group of patients with a mean BOP of < or = 20%, only 1/5 of the loser sites were found. This clearly indicated, that patients with a mean BOP of < or = 20% have a significantly lower risk for further loss of probing attachment at single sites.