Fourteen cases of acute lobar atelectasis were alternately allocated to one of two chest physiotherapy regimens for treatment. Treatment in group 1 comprised positioning, vibrations, hyperinflation, and suction, and in group 2, treatment consisted of hyperinflation and suction alone. Treatment in either group was given hourly for six hours. Patients in group 1 had a significantly higher mean percentage resolution of their atelectasis (mean value, 60.1 percent), as seen on chest roentgenogram, after one treatment intervention than patients in group 2 (mean value, 7.6 percent; p less than .006). After the intensive six-hour treatment period, the difference between the groups was marginally statistically significant, still favoring group 1 over group 2 (p less than .055). Follow-up roentgenograms at 24 and 48 hours revealed no significant difference between the treatment groups (p greater than .10 and greater than .20, respectively). These results suggest that, at least initially in the course of acute lobar atelectasis, positioning and vibrations add to the efficacy of a treatment of hyperinflation and suction alone.