C1498 is an atypical myeloid leukemia that originated in a C57BL/6 mouse and has been used as a model for acute myelogenous leukemia. In studies of the immune response to C1498, we found that this tumor contained mRNA encoding the canonical NKT cell receptor V β 8.2-V α 14J α 281. Although cell-surface phenotypic analysis showed C1498 to be negative for NK1.1, it expressed several other molecules associated with NKT cell populations, such as DX5, CD1d, CD69, CD44, CD45RB and B220. RT-PCR demonstrated that C1498 contained CD3 ϵ mRNA transcripts, but message was not found for CD4, CD8 α, or CD8 β. This indicates that C1498 falls within the double negative (CD4 ⁻ CD8 ⁻ ) NKT cell lineage. RNase protection analysis showed that C1498 expressed mRNA for IL-2, IL-15, and macrophage migration inhibitory factor (MIF). These findings suggest that C1498 should be re-classified as a NKT cell leukemia with atypical myeloid features. It may, therefore, be a novel cell line in which to study NKT cell development and serve as a model for human NKT cell malignancies.