[en] Tl-201 SPECT was used to evaluate 40 cases of pulmonary nodule between 10 mm and 30 mm in diameter. In benign and malignant lesions, 12/20 cases and 18/20 cases showed positive accumulation respectively. The benign lesions with negative accumulation ranged in every size, whereas malignant lesions with negative accumulation were limited to less than 20 mm. The retention index of benign lesions (-4.7±11.0%) was lower than that of malignant lesions (21.3±11.5%) (p<0.01). The results suggest that Tl-201 SPECT is useful for diagnosing small pulmonary nodules, though those cases were limited, especially in cse of negative results on histological examination. (author)