Translocation (11;14)(q13;q32) is a recurring chromosome abnormality which is found non-randomly in non-Hodgkin's lymphoma, especially of follicular type, as well as in B-cell chronic lymphocytic leukaemia, Waldenström's macroglobulinaemia and multiple myeloma. To define further the prevalence of this abnormality in multiple myeloma, we studied a series of 17 patients with this disease with concomitant chromosome analysis and Southern blotting, using a probe specific for the major translocation cluster of the BCL-1 oncogene which is located at chromosome 11q13. Karyotype analysis of 14 evaluable patients revealed three cases with abnormalities of chromosome 11q13, two of them with t(11;14)(q13;q32) and one with del (11)(q13). Southern blot analysis showed no rearrangements in BclI and HindIII digests of DNA from 17 patients including the three patients with anomaly of chromosome 11q13, using a BCL-1 specific probe. A possible restriction length polymorphism was detected in EcoRI cut DNA of five out of 11 patients studied. Therefore the chromosomal break point in our cases with abnormality of chromosome 11q13 must lie outside the major translocation cluster of the BCL-1 gene. However, in centrocytic lymphoma rearrangement of the BCL-1 oncogene has been detected in up to 50% of cases. Location of the break point may therefore be dependent on the differentiation of the transformed B-cell.