1. Six groups of 45-day-old, 23.0 +/- 1.7 g, female Balb/c mice were inoculated intraperitoneally with 63, 252, 440, 630, 2520 or 6300 I.U. of vitamin D for 6 days. A seventh group was inoculated with saline. Each group consisted of 30 animals. 2. All animals inoculated with the doses of 2520 and 6300 and 70% of mice which received 630 I.U. of vitamin D died 21 days after the first administration of the vitamin. The LD50 was 630 I.U. 3. The survivors were divided into two groups inoculated intraperitoneally with 5000 trypomastigotes of either Y or CL strain of Trypanosoma cruzi. 4. Based on the survival index on day 73 after infection, Vitamin D gave statistically significant protection (P < 0.01) for mice inoculated with doses of 63 or 430 I.U. of Y or CL strains, respectively. 5. On histopathological examination, inflammatory reaction and cellular and tissue parasitism were less intense in animals which received higher doses of vitamin D. 6. It is concluded that an overload of vitamin D had a protective effect against CL and Y strains of Trypanosoma cruzi infection in Balb/c mice.