The present invention relates to a series of substituted aza-indole derivatives of the formula I: wherein R, R.sub.1, R.sub.2, R.sub.3, R.sub.4, X and Y are as defined herein. This invention also relates to methods of making these compounds. The compounds of this invention are inhibitors of poly(adenosine 5'-diphosphate ribose) polymerase (PARP) and are therefore useful as pharmaceutical agents, especially in the treatment and/or prevention of a variety of diseases, including diseases associated with the central nervous system and cardiovascular disorders.