1. In rabbits receiving subcutaneous injections of benzene, the simultaneous administration of sulfapyridine, per os, prevented the development of leukopenia. The sparing effect of sulfapyridine on the intoxication of the leukopoietic tissue by benzene was demonstrated not only by the range of daily leukocyte counts but also by microscopic examination of the bone marrow of treated animals.
2. The administration of para-aminobenzoic acid failed to inhibit the leukotoxic action of benzene.
3. The administration of sulfapyridine alone to rabbits was followed by daily variation in the number of leukocytes in the circulating blood but persistent leukocytosis was not observed. The inhibiting action of sulfapyridine was not found to be referable to the development of an overcompensating leukocytosis.
4. In preliminary experiments, the excretion of phenols by rabbits receiving sulfapyridine together with benzene differed from that observed in animals receiving benzene alone. In the former group, the rise in the excretion of total phenols was not so high as in the latter group, but the percentage of combined phenols was greater. The possible significance of the findings has been discussed.