T-cell receptor genes are found in the germ-line configuration as well as in rearranged forms, as detected in T lymphocytes by different patterns in Southern blot analysis. We have recently shown that cytotoxic T-lymphocyte (CTL) "precursor" clones, in which rearrangements are not detected in the gene encoding the T-cell receptor alpha-chain (TCRA), acquire specific lytic function induced by treatment with recombinant interferon alpha or gamma. We now report that, coincident with the acquisition of cytotoxic function by the precursor CTL clone; recombinant interferon alpha appears to induce a rearrangement of TCRA. In addition, in a mature CTL clone (i.e., one already showing lytic function) in which one TCRA allele is rearranged, treatment with recombinant interferon alpha appears to induce a new rearrangement of a TCRA gene.