Bilateral bone‐marrow examinations from the posterior iliac crests were routinely performed as a pretreatment staging procedure in 89 consecutive patients with small‐cell anaplastic carcinoma of the lung. Bone‐marrow involvement was found in 20 patients (22.5%), in 9 (10.1%) only on one side, and in 11 (12.4%) on both sides. Aspiration was found to be significantly superior to biopsy, being positive in 25 examinations as compared with 14 positive biopsies. Compared with unilateral bonemarrow examination the positive findings increased by approximately 30%. Bilateral bone‐marrow examinations are recommended in patients in whom the detection of bone‐marrow metastases will have therapeutic imp