Fine-needle aspiration biopsy of the spleen was carried out in 557 patients. In 381 cases, the aspiration was performed because of suspected sarcoidosis. The sensitivity of the technique was 59 percent and the specificity 97 percent. The cytologic picture of the spleen was abnormal in 184 patients with sarcoidosis and in seven patients with extrinsic allergic alveolitis. No major complications occurred. The method provides a simple, safe, quick, and reliable way of producing evidence of a granulomatous process in patients with suspected sarcoidosis. The biopsy method can be used with advantage before application of more invasive techniques.