Libraries of new, small peptoid monomers and dipeptoids were synthesized and assayed for antiproliferative activity against representative human neoplastic cell lines. The C-terminal N-alkyl amide peptoids are cytotoxic and are the smallest peptoids reported to have such activity. These compounds were conveniently synthesized on a BAL resin. Owing to their structure, the peptoids did not suffer from DKP formation, a problematic side reaction typically observed in peptide and peptoid synthesis.