The subacute toxic effects of dietary T-2 toxin (20 ppm) incorporated in semipurified diets of 8%, 12% or 16% protein, were examined in young Swiss mice after one, two, three and four weeks. Dietary T-2 toxin caused substantial reductions in growth and food consumptaion, the degrees of which were greatest in mice fed the diets of reduced protein content. T-2 toxin consistently caused similar degrees of nonregenerative anemia, lymphopenia, thymic atrophy and gastric hyperkeratosis irrespective of the dietary protein level. However, erythroid hypoplasia was temporary in mice fed T-2 toxin in the 16%-protein diet such that erythroid precursors regenerated in splenic and bone marrow and were hyperplastic after four weeks. Liver to body weight ratios of mice fed T-2 toxin in the 16%-and 12%-protein diets increased during the four week trial in comparison to control mice fed at a similar rate. These observations indicated that suppression of erythropoiesis in mice by dietary T-2 toxin was temporarty and that the interval before regeneration was prolonged by diets of reduced protein content.