Seventeen young adult albino Norway rats were experimentally inoculated with Toxoplasma. None died of the infection. Thirteen showed parasitemia indicating that infection had occurred. All rats gave negative responses to the Sabin-Feldman dye test prior to inoculation. All responded positively in from 4 to 7 days after inoculation. Median peak titer of 1:4096 was reached on the 15th day. Median titer after 2 mos. was 1:256 and after one year 1:16. In most rats positive response continued throughout the life of the rats; maximum followup was 620 days. In one exceptional rat the peak titer reached was 1:64 and the serologic response was absent by the 65th day after inoculation. Application of the observations to field findings is discussed.