The effect of manual chest percussion was studied in nine patients with copious sputum production. Treatment consisting of postural drainage (PD) and the forced expiration technique (FET) produced sputum at the rate of 0.831 g min-1. When percussion was included in the treatment regimen, the rate of sputum production was significantly greater (P less than 0.05), being 1.231 g min-1 for fast percussion and 1.040 g min-1 for slow percussion. Pulmonary function and oxygen saturation were unaffected by any of the treatment regimens. This study demonstrates that manual chest percussion is a useful adjunct to PD and FET in the treatment of patients with copious sputum production.