Selective pairwise interactions between a number of CD3 chains and the clonotypic T cell antigen receptor (TCR-alpha, -beta) chains have recently been reported. What still remains unanswered is the site of interaction between TCR-beta and CD3-gamma chains. To examine the region of interaction between TCR-beta and CD3-gamma chains, a variety of genetically altered TCR-beta and CD3-gamma chains were constructed using recombinant cDNA techniques. Non-T cells (COS-7) were transfected with cDNA constructs, metabolically labelled, and immunoprecipitates were analysed for assembly using non-equilibrium pH gel electrophoresis (NEPHGE)/SDS-PAGE. The results demonstrated that assembly between TCR-beta and CD3-gamma chains was localized to their extracellular domain. These findings, when coupled with the information on pairwise interactions and formation of higher order subcomplexes, extend our model of the structure of the TCR complex.