Secretory heterohybrid clones from seven pristine human B cell lymphomas of diverse histologic types were established to investigate the question of tumor clonal diversity. We found that in six tumors, heterohybrid-derived Ig showed similar band patterns in IEF; families of anti-Id prepared from tumor Ig reacted uniformly with individual heterohybrids and original tumor; and the V gene loci displayed little variation on Southern analysis. In one patient who was followed with serial multiple site biopsies over a 14-mo period, clonal Id was preserved until the final stage of his disease, in spite of cytotoxic treatment. In a single follicular tumor (J.M.), each of the anti-Id reacted uniformly with the parent tumor and the individual heterohybrids, except that three of six clones failed to react with a single anti-Id family member. A Southern analysis of the VH gene locus revealed an identical gene rearrangement that was shared by the parent tumor and each heterohybrid. However, there was considerable heterogeneity of J.M. heterohybrid Ig in IEF gels, and we demonstrated the production of variant lambda L chains by the heterohybrid clones. One type of lambda L chain had a normal mobility in SDS-PAGE gels but larger lambda variants were produced by four of six heterohybrids. A Southern analysis of the VL gene displayed considerable variation in the type of lambda rearrangement present in the various heterohybrids, suggesting extensive diversity at the VL gene locus. In a second tumor (S.C.) that exhibited uniform anti-Id tumor reactivity we were also able to demonstrate the presence of a second minor tumor cell population (a biclonal tumor). Our data suggest that intraclonal VH variation may vary considerably with lymphoma subtype and mutagenic exposure and that an additional mechanism for generating spontaneous intraclonal heterogeneity is genetic variation at the VL locus.