UNLABELLED A scintigraphic model of the lungs was used to study the threshold of detection of diffuse disease of the lungs. METHODS Randomly distributed cold lesions of 4, 8, 12 and 16 mm3 block sizes were created, occupying 0%-50% of lung tissue in steps of 1%. These were submitted for reporting to five observers each with a normal study for comparison. RESULTS No observer detected lesions of 4-mm3 block size even when up to 50% of the lung was involved. All observers detected lesions of 8-mm3 block size when a mean of 27% of lung tissue was involved with lesions. As lesion size increased to 12 and 16 mm3, observers detected lesions when a mean of 10% and 6% of lung tissue was involved, respectively. Comparison between views for each observer showed that the lateral and anterior oblique views were used more often than the anterior, posterior oblique and posterior views. CONCLUSION This model suggests that pulmonary scintigraphy has the potential to detect a diffuse disease such as emphysema at an early stage of lung involvement. In general, small anatomic lesions appear to have more profound scintigraphic consequences. However, even scintigraphic lesions of the order of size of the pulmonary acinus are easily detected.