Of 668 consecutive patients with SCLC, 472 underwent bone marrow examination for staging. In 330 patients a triple examination (sternal aspiration, iliac crest aspiration and biopsy) was performed, otherwise a single procedure. Bone marrow infiltration (MI) was found in 37% of the patients with extensive disease, and the frequencies of a positive finding in single and triple examination were not statistically different. In the group having triple examination performed iliac crest aspiration alone disclosed MI in 32%. When all three procedures were included still more patients with MI were found (42%) but the two values were not significantly different. In 6.6% of patients who would have been classified as 'limited' did bone marrow examination change the stage to extensive disease. Based on these results we recommend iliac crest aspiration, but not triple examination with iliac crest biopsy, in the staging of SCLC.