Over a period of 3 yr, a series of ten NK clones that express a unique clonotypic T cell receptor-like structure, termed NKTa, has been generated from a single individual. These clones were derived from either peripheral blood nonadherent cell fractions (JT9, JT10, JT11), NKH2-purified cells (CNK8, CNK9), or NKTa-purified cells (CNK11, CNK12, CNK13, CNK14, CNK15). Flow cytometric analysis of peripheral blood mononuclear cells from this individual showed that NKTa+ cells occur with a frequency of approximately 0.15%. The existence of NKTa+ cells in peripheral blood was confirmed by use of immunorosette enrichment techniques, flow cytometric purification, and subsequent clonal expansion of NKTa+ cells. Phenotypic analysis of NKTa+ clones showed that all expressed NKH1 as well as T3, T8, T11, T12, and Mo1 antigens. Only five of ten clones expressed NKH2 antigen. All NKTa+ clones had broad cytolytic activity against a series of seven different target cells that was similar to that of other NK clones. In addition, cytotoxicity of each clone could be inhibited by preincubation of effector cells with monoclonal anti-NKTa or by preincubation of target cells with monoclonal anti-TNKTAR. Although half of the NKTa+ clones appeared phenotypically different from the other half with regard to the expression of NKH2 antigen, analysis of T cell receptor gene rearrangements indicated that all NKTa+ clones contained identical gene rearrangements of C beta 2.