A series of clones of human natural killer (NK) cells was characterized with respect to expression of the Ti alpha and Ti beta genes of the T-cell receptor. T11+T3+ NK clones contained Ti alpha and Ti beta RNA transcripts and expressed disulfide-linked heterodimers, demonstrating the presence of a functional T-cell receptor. In contrast, T11+T3- NK clones expressed only 1.0-kilobase truncated Ti beta transcripts, without a Ti alpha transcript and no detectable surface Ti protein. Since previous studies demonstrated that Ti beta gene activation precedes Ti alpha gene activation in thymic ontogeny, the T11+T3- NK cells appear to be derived from T-lineage precursors.