Leukemia incidence for mice in the latent phase of Friend virus disease. Mice were fed folate-free and control diets as described in the Materials and Methods and the Fig 1 legend. Mice were infected with Friend virus on day 0 and monitored for the subsequent year for the development of acute leukemia. The numbers of mice in each group that entered the latent part of the preleukemic phase as defined in results were 63 for controls, 63 for folate-deficient 1, and 44 for folate-deficient 2. All deaths were due to leukemia except for 1 mouse of the folate-deficient 2 group that was killed on day 238 (shown as +) with severe ascites and cystic kidneys, but normal liver, spleen, and WBC. This mouse was censored for statistical analysis.