Cytogenetic, in situ hybridization, and molecular studies were performed in a case of T-cell-rich B-cell lymphoma. Demonstration of Ig gene rearrangements for both heavy and light chains confirmed the B-lineage restriction of the neoplastic cell population. Moreover, as expected in B-cell malignancies, all abnormal karyotypes showed a 14q+ chromosome marker involving 14q32. The origin of the extra material on the derivative 14q+, as defined by chromosome painting with a library for chromosome 11, and Southern blotting for c-myc and bcl-2 rearrangements, remains unknown.