Mutant T cell lines that do not express the endogenous alpha- and/or beta-chain genes of the TCR were generated from the alpha beta TCR/CD3+ tumor cell line C6VL with a combination of classical mutagenesis methods and selection of somatic hybrid variants. This novel strategy obviated the need for repeated mutagenesis and screening of a large number of individual clones. The loss of either the alpha- or the beta-chain expression in the mutant cells was associated with the loss of surface TCR/CD3 complex, which could be rescued by the transfection of appropriate exogenous alpha- and/or beta-chain gene constructs. Because these cells express a single TCR molecule on the cell surface, they are useful for the study of the assembly and function of the alpha beta TCR. This strategy is also generally applicable for the generation of homozygous mutant cell lines lacking other gene products.