Chromosomes were studied in 33 untreated myeloma patients, and results were correlated with the class of Ig secreted by the myeloma cells. A high incidence of clonal karyotypic anomalies seemed to be present in IgG3 myeloma patients, in whom the disease was advanced at diagnosis and rapidly progressing. Among the chromosome anomalies, the t(11;14)(q14;q32) was particularly prominent, and this chromosome anomaly, in analogy with the Ph1 chromosome, may characterize a family of lymphoproliferative disorders.