The T lymphocytes from mice recovering from infection with lymphocytic choriomeningitis virus were selected for subclasses by treatment with anti-Lyt antisera and complement. Lyt-23 cells and mixtures of lyt-1 and Lyt-23 cells caused up to one-half the destruction of cultivated target cells as compared with untreated T lymphocytes; Lyt-1 cells alone were not cytotoxic. Selected and unselected spleen T cells were also inoculated intravenously into previously infected mice. Whereas unselected cells reduced infectious virus in the spleens of the recipients approximately 100-fold, only marginal effects, which were not preferentially associated with one particular subclass, were seen with selected LYT-23 or Lyt-1 lymphocytes or a mixture of both. Apparently the Lyt-23 cells, shown to by cytolytic for infected cells in vitro, did not cause elimination of a measurable quantity of the virus from mice.