Condensation of indole with acetone in ethanolic hydrochloric acid gave five products, one of which was the easily autoxidizable monobase Ib. Acetylation and methylation of Ib was accompanied by loss of a molecule of hydrogen, giving the diacetyldehydro (IVa) and dimethyldehydro (IVb) derivatives. Condensation of 1-methylindole with acetone gave the same dimethyldehydro derivative (IVb), as well as the bisindole Va in larger yield, while condensation with mesityl oxide gave, depending upon the mole ratio, the 1:1 adduct VIb or the bisindole Va, along with 1-methylindole trimer. Reaction of indole with mesityl oxide gave the 1:1 adduct VIa. Heating of VIb at 140–150° gave a 2:1 condensation and rearrangement product (Vb or IX). Condensation of 1-methylindole with methyl isobutyl ketone gave a 2:2 product, probably XII or XIII, and a 1:2 product, possibly XIV or XV. Attempted cyclization of the 1:1 adduct of indole and methyl vinyl ketone gave two crystalline bimolecular condensation products, a neutral acyclic product (XVIII), and a basic cyclization product which is an indoline derivative, possibly XX.