A number of N-hydroxylated indole derivatives have been fed to rats and the urinary metabolites compared with those obtained on feeding the corresponding N-H indoles. 1-Methoxy- and 1-acetoxy-indole were metabolized to compounds normally observed on feeding indole. 1-Hydroxy- and 1-methoxy-indole-3-carboxylic acids were both partially excreted unchanged and reduced to indole-3-carboxylic acid which was excreted along with its glucuronide. Indole-3-glyoxylic acid and its 1-methoxy derivative were excreted almost entirely unchanged. 1-Hydroxyindole-3-glyoxylic acid was mostly excreted unchanged, but some reduction to indole-3-glyoxylic acid took place. The stability of these acids is associated with their low pKa values. The significance of the removal in vivo of groups attached through oxygen to the 1 position of indoles in relation to the synthesis of new potential medicinal agents is noted.