In 43 patients with cystic fibrosis, the results of 122 Tc-99m DTPA aerosol ventilation (DAV) studies were compared with pulmonary function tests (PFTs) that were performed within 24 hours of the DAV studies. The DAV studies were evaluated blindly for (A) number of pulmonary segments showing little or no ventilation, (B) number of foci of bronchial deposition of aerosol, and (C) subjective overall improvement, lack of change, or worsening from the previous study. (A) and (B) correlated significantly with all PFTs (p's <.001, r's = -.51 to -.73). Changes in (A) and (B) also correlated with changes in PFTs (p's ≤.001, r's = -.37 to -.58). The three populations in (C) were significantly different from each other with respect to changes in all PFTs (p ≤.002). Intervals between studies showing subjective improvement, no change, and worsening averaged 60, 133, and 306 days, respectively. These results suggest that DAV is an indicator of both regional and global pulmonary function and may be useful in evaluating patients with cystic fibrosis.