A therapeutic trial with "minute" and "titrated" doses of folic acid was performed in 30 patients with the megaloblastic anemia of tropical sprue. Eleven patients responded hematologically to 25 µg. daily doses of the vitamin; nine patients responded to "titrated" doses ranging from 75 to 250 µg. daily. Eleven patients failed to respond to either "minute" or "titrated" doses of the vitamin. The implications and possible reasons for the success or failure of microdoses of folic acid in sprue were discussed.