Tetrahymena geleiiW is not inhibited by either 4-amino-pteroylglutamic acid or N10-methylpteroylglutamic acid. Moreover, both of these analogs promote growth in the absence of folic acid. It is suggested that the organism possesses enzymes which deaminate the 4-position and enzymes which demethylate the 10-position. Pteroyl-aspartic acid and 4-amino-pteroylaspartic acid spare, but do not replace, folic acid. Citrovorum factor is never more active, and usually less active, than folic acid.