Long-term cultures of bone marrow from 15 cases diagnosed previously with primary solid tumors were analyzed cytogenetically. Of these cases, 10 had normal karyotypes and five had chromosomal abnormalities. Trisomy 5 was found in four cases, three with trisomy 5 as the only change and one with trisomy 5 and trisomy 12. These results suggest that trisomy 5 may be a nonrandom change associated with an in vitro or in vivo phenomenon.