Two splenic cell clones were derived from mice bearing UV-induced skin tumors; both clones are I-J+, Thy-1+, and J11D+. Cellular extracts, but not culture supernatants, from the two clones, designated T4 and T5, specifically suppress primary cytotoxic and proliferative responses to UV-induced tumor targets. Therefore, clones T4 and T5 would appear to function as putative I-J+ suppressor cells with specificity for an antigenic epitope common to several UV-induced tumors. To derive more information concerning the status of Ag-receptor genes in the suppressive clones, we analyzed the rearrangement and expression of Ig and TCR genes. The first clone, T4, expressed Thy-1, a T cell-surface marker, yet it had not rearranged its TCR-beta, -gamma, and -delta gene families, nor were TCR-alpha, -beta, -gamma, or -delta transcripts detectable. Instead, clone T4 contained rearranged Ig H chain genes and expressed mu RNA. Because neither lambda nor kappa L chain transcripts were detected, this clone could not utilize a complete Ig molecule as its Ag receptor. On the other hand, clone T5 contained exclusively TCR gene rearrangements; it expressed alpha and beta transcripts of the correct sizes. However, the level of RNA that could encode the delta-chain of the CD3 accessory molecule was below detection, so it is unlikely that this TCR was expressed on the cell surface. The rearrangement of Ig genes in one clone and TCR genes in the other clone does not necessarily indicate that these genes encode the Ag receptors used by these clones. However, it suggests either that suppressor-like cells can derive from different lymphocyte precursor lineages or that rearrangements of the known TCR genes or the Ig genes are irrelevant to the function of this cell lineage.