The isolation and structural characterization of three new heterocyclic and macrocyclic peptides, balgacyclamides A-C, from Microcystis aeruginosa EAWAG 251 are reported. The constitutions were determined by 2D-NMR methods and mass spectrometry, and the configurations were assigned after ozonolysis and hydrolysis by HPLC-MS methods using Marfey's method as well as GC-MS using authentic standards. Balgacyclamides A and B were active against Plasmodium falciparum K1 in the low micromolar range, while displaying low toxicity to rat myoblasts. The isolation and structural characterization of three new heterocyclic and macrocyclic peptides, balgacyclamides A-C from Microcystis aeruginosa EAWAG 251 is reported. The constitution was determined by 2D-NMR methods and mass spectrometry and the configuration was assigned by HPLC-MS methods using Marfey's method as well as GC-MS using authentic standards. Balgacyclamides A and B were active against Plasmodium falciparum K1 in the low micromolar range, while displaying low toxicity to rat myoblasts.