Chromosomes of six patients with plasma cell leukemia and one patient with leukemic macroglobulinemia were examined from peripheral blood, bone marrow, and/or pleural fluid. All the patients had a clonal chromosomal abnormality. The modal chromosome number was near tetraploid in two, pseudodiploid in two, and hypodiploid in three patients. Rearrangements of chromosome 1 were found in all the patients. The most consistent abnormality was a large marker involving the long arm of No. 1, found in

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... x patients, including the patient with macroglobulinemia. Each patient had one to four large markers which resulted in partial trisomy to hexasomy for the long arm of No. 1. The translocations occurred with No. 9 in two, with No. 16 in two, and Nos. 8, 17, and 18 each in one patient. The survival time from the diagnosis was less than 1 year in five of them and over 2 years in one. The only patient whose cells lacked an extra 1q lived for over 3 years. Five 14q+ marker chromosomes were detected in three patients. The donor chromosome was No. 11 in one of these and was undetermined in the others; the size of each 14q+ marker seemed quite different which suggested different donor chromosomes. Loss of a sex chromosome was found in five patients. Loss of No. 13 and gain of No. 7 or 7q were each found in two patients. Rearrangement or deletion of the short arm of No. 8 was found in five patients. A rearrangement of 9p was found in three patients. The myeloma cells had a different morphology in the peripheral blood, bone marrow, and/or pleural fluid before and after the leukemic phase of one patient; however, chromosome analysis revealed the same clone despite the altered morphology.