We examined the lg heavy chain variable region genes (Ig V(H) genes) expressed in biopsy specimens of 10 patients with acquired immunodeficiency syndrome (AIDS)-associated lymphoma. Eight expressed Ig V(H) genes of the V(H)4 group, indicating a bias toward expression of Ig V(H) genes of this subgroup. Sequence analyses of Ig V(H) genes isolated from any one lymphoma did not reveal evidence for intraclonal diversity. However, some lymphomas express Ig V(H) genes that apparently have undergone somatic diversification and selection. In addition, we found that the sequence encoding each examined third complementarity determining region most likely resulted from D-D fusion, a process that ordinarily contributes to the generation of a relatively small proportion of the Ig heavy chain genes expressed by normal adult B cells. The noted restriction in the use of Ig V(H) genes by AIDS-associated B-cell lymphomas suggests that antigenic stimulation contributes to lymphomagenesis in patients with AIDS.