AbstractThe reactivity of hydroxy‐indoles under the conditions of the Mannich‐reaction has been studied. The electrophilic side‐chain enters in each case in a position ortho to the phenolic group. 4‐Hydroxy‐indole is substituted in the 5‐, 5‐hydroxy‐indole in the 4‐, 6‐hydroxy‐indole in the 7‐, and 7‐hydroxy‐indole probably in the 6‐position. The structures of the Mannich bases from 4‐, 5‐ and 6‐hydroxy‐indole have been confirmed by comparison of the hydroxy‐methyl‐indoles obtained by reductive desamination with hydroxy‐methyl‐in