Novel peptoid oligomers are disclosed that have a formula represented by the following formula I: wherein R1 and n are as described herein. The peptoids demonstrate antimicrobial and antimalarial activity and may be prepared as pharmaceutical compositions and used for the prevention or treatment of a variety of conditions in mammals including humans where microbial or malarial infection is involved. The present cyclic peptoids are particularly valuable as their effect is rapid, broad in spectrum and mostly indifferent to resistance provoked by standard antibiotics.