The 4-amino analogue of pteroylglutamic acid was fed to mice as a dietary supplement. There was some indication of reversal by pteroylglutamic acid of the effect on mice when the level of the antagonist was 0.3 part per million of diet. Death was found to occur within a few days with levels of 1 part per million of diet or higher. The effect was not reversed by feeding high levels of pteroylglutamic acid. This finding may be contrasted with the inhibitory effect of the 4-amino compound on S. jecalis R which is reversed by pteroylglutamic acid.