Changes in spirometry during consecutive admissions for treatment of pulmonary infective exacerbations were studied in 45 patients (24 males, 21 females) with cystic fibrosis (CF) who had required five or more such admissions. Over the overall study period there was a mean (SD) decline in FEV1 of -112.1 (188.0) ml yr-1 (P less than 0.001) and in FVC of -47.9 (82.4) ml yr-1 (P less than 0.001). FEV1 and FVC increased during each admission with treatment; however, the magnitude of this change became less over consecutive admissions by a mean value of -33.3 ml (45.0) (P less than 0.001) for FEV1, and -26.0 (72.2) ml (P less than 0.05) for FVC. In the majority of patients that died or underwent transplantation, FEV1 at the time of the last admission did not rise above 800 ml despite full treatment.