Melanocortin receptor-specific piperazine or ketopiperazine compounds having the structure: ##STR00001## and stereoisomer and pharmaceutically acceptable salts thereof, where X is CH.sub.2 or C.dbd.O, R.sub.1, R.sub.2, and R.sub.3 are as described in the specification, preferably where R.sub.3 is a D-amino acid with at least one substituted or unsubstituted phenyl or naphthyl aromatic ring, and where R.sub.3 optionally further includes an amine capping group, a second amino acid residue or a second amino acid residue with an amine capping group, which compounds are agonists, antagonists or mixed agonists and antagonists at one or more melanocortin receptors, and having utility in the treatment of melanocortin receptor-related disorders and conditions. Methods of synthesis of compounds of structure (I), pharmaceutical compositions containing a compound of structure (I) and methods relating to the use thereof are also disclosed.