Human T cell hybridomas were produced by fusing the hypoxanthine phosphoribosyltransferase-deficient line of the human T cell lymphoma Jurkat with a continuous line of normal human T cells specific for tetanus toxoid (TeT). The hybridomas were selected for their ability to produce interleukin 2 after exposure to TeT on semiautologous monocytes and for their ability to bind to TeT-pulsed semiautologous monocytes. These antigen-specific T hybridomas demonstrated potent helper activity for semiautologous B cells as determined by the production of high levels of anti-TeT antibody in vitro.