Activated 3-substituted-4,6-dimethoxyindoles undergo acid catalyzed condensation with acetone and acetophenones in the presence of hydrochloric acid to give pyrrolo[a]indoles. Mixed pyrrolo[a]indoles can similarly be formed using a 1:1 mixture of two indoles. The reaction was found to be sensitive to acidity, with a 3:2 spiro condensation product being preferentially formed in the presence of p-toluenesulfonic acid.