Healing events after nonsurgical periodontal therapy in patients with periodontal pockets 4--7 mm deep were investigated. Incisors, cuspids and premolars in 15 patients were treated by plaque control and supra- and subgingival debridement using hand or ultrasonic instruments in a split mouth approach. The results were evaluated by recordings of plaque scores, bleeding on probing, probing pocket depths and probing attachment levels. All these parameters were improved during the initial 4--5 months after start of therapy. Little change occurred during the rest of the 13-month observation period. No difference of results could be observed comparing hand and ultrasonic instrumentation or comparing the results of two different operators. Initially a total of 106 sites demonstrated probing pocket depths greater than or equal to 6 mm. At 13 months only 13 such sites were observed. The apparently successful results of conservative treatment of patients with 4--7 mm deep pockets in the present study raise the question to what extent nonsurgical therapy is feasible also in patients with severely advanced lesions.