A follow-up study was conducted in 40 children who had been enrolled in a prospective randomized study of exogenous surfactant therapy for respiratory distress syndrome (RDS) (n = 22; S) or placebo (n = 18; P) to determine long-term pulmonary sequelae of surfactant treatment in premature infants with RDS. At follow-up, mean (SD) age was 6.63 (0.18) and 6.55 (0.23) years for S and P, respectively. Complete lung function tests (LFT) were attempted in all patients. Satisfactory data were obtained in 17/22 surfactant-treated and in 12/18 control children. There was no significant difference between groups for any of the parameters measured. Mean (SD) functional residual capacity (FRC) was 92% (16%) and 90% (21%) predicted, mean (SD) airway resistance (R(aw,exp)) was 122% (25%) and 127% (61%), and mean (SD) forced expiratory volume in 1 s (FEV1) was 104% (12%) and 99% (17%) predicted for S and P. Only maximal expiratory flow at 25% vital capacity (L/s) was significantly below the predicted range in S and P groups, with 74% (23%) and 77% (28%), respectively. To test bronchial hyperreactivity, a simple standardized running test was performed: 4 children in S and 5 in P showed a significant response as defined by clinical airway obstruction or changes in FEV1 and/or R(aw), with no significant difference between groups. Although we found no major abnormalities in lung function and no difference between S and P at early school-age, lack of cooperation during lung function tests makes further follow-up necessary.