These findings show that the administration of vitamin B12 to patients with tropical sprue was followed by general clinical and hematologic improvement provided the dosage was adequate. A single dose of 4 micrograms administered in case 4 produced little or no change. The larger dosage of 10-25 micrograms administered in the other cases was accompanied by striking increase in strength and vigor and a decrease in the diarrhea; however, in no instance was a maximal dose given and these patients quickly tended to relapse clinically and hematologically. They could be relieved promptly again either by another injection of vitamin B12 or by a compound of folic acid. (The conjugated compounds of folic acid used in these cases were used for experimental purposes, and they produced the same hematologic response as that of folic acid per se.) Case 3, who had an excellent hematologic response after eating one serving of 400 grams of liver, is regarded as especially significant in that it suggests that, as powerful as vitamin B12 is as a therapeutic agent, it is more effective when given with liver. It is especially noteworthy that cases 1 and 2, who had three injections of vitamin B12, have had steady clinical and hematologic improvement. The reader should have in mind that a single injection of approximately 100 micrograms of vitamin B12 probably would be needed to produce a full hematologic response in persons so ill. This tentative appraisal would suggest that this therapeutic compound, per unit of weight, is more effective in treating human disease than any compound that yet has been used.

ACKNOWLEDGMENT We are very much indebted to others who have aided us in selecting cases and in observing results. Especially we wish to thank Dr. F. Hernandez-Morales, Dr. Hector Marchand, Miss Clemencia Benitez-Gautier, and Miss Sara Torres.