The association of ankylosing spondylitis (AS) and lung parenchyma abnormalities has been shown in previous studies by radiological and pulmonary function tests. Technetium-99m diethylene triamine pentaacetic acid Tc-99m-DTPA) dynamic lung scanning is an easy, noninvasive method to assess alveolar-capillary barrier permeability. We aimed to study the abnormalities in pulmonary clearance of Tc-99m-DTPA in patients with AS, and the presence of any correlation between this clearance and the radiological and pulmonary function tests. We studied twenty-one nonsmoker patients with AS who were compared to 21 age and sex matched healthy volunteers. All subjects underwent pulmonary function tests and pulmonary scintigraphy with Tc-99m-DTPA to evaluate pulmonary clearance. Clearance half time (T-1/2) of Tc-99m-DTPA through the lungs was calculated by placing a monoexponential fit on the 30 min activity curves. High resolution CT and pulmonary function tests were performed for each patient. Our results showed the following: Spirometric parameters of forced vital capecity (FVC) and the ratio of forced expiratory value in 1sec/FVC (FEV1%) scores were worse in patients compared to the control group (P<0.005 and P<0.05, respectively). Clearance half time was longer in AS group than in the control group (58.45 +/- 7.59 and 51.62 +/- 4.79 min, respectively; P<0.05). There was a negative correlation between T-1/2 Value and FEV1% (r=-0.876, P < 0.01), of AS patients and the control group. Additionally, there were moderate positive correlation between T-1/2 and FVC (r=0.705, P<0.001), weak positive correlation between T-1/2 and FEF2575 (r = 0.493, P<0.05), and T-1/2 and DLCO (r=0.444, P<0.05). A positive correlation was found between the duration of the disease and T-1/2 (r=0.44, P < 0.05). In conclusion, longer T-1/2 values and lower FVC values in nonsmoker AS patients may suggest not only the pulmonary involvement in AS but also the duration of the disease.