Of 95 young patients with non-Hodgkin's lymphoma treated at the National Cancer Institute on Pediatric Branch Protocol 7704, 18 (18.9%) had bone marrow involvement prior to treatment. Their mean age was 20.5 years. Twelve patients had small, non-cleaved lymphoma (ten Burkitt's and two undifferentiated, unspecified), five had lymphoblastic lymphoma, and one had a diffuse large cell lymphoma. All had extensive disease. We obtained bilateral bone marrow biopsy specimens, touch preparations, clot sections, and aspirate smears from 13 of the 18 patients. When paired contralateral samples were reviewed, in as many as six out of ten of the pairs only one side was positive for tumor. When paired ipsilateral samples were similarly reviewed, in as many as seven out of 21 of the pairs only one specimen was positive for tumor. The biopsy specimen was the most useful of the four types of study performed, yielding positive results in 87% of the preparations. Thus, in a high percentage of patients, multiple marrow sampling revealed disease that might have been missed if fewer specimens had been obtained. Only four of our 18 patients (22.2%) had long-term remissions. Because young patients with marrow disease are at high risk and may be eligible for more intensive treatment protocols, we recommend that staging should include bilateral bone marrow biopsies and bilateral aspirates.