Five new cyanobacterial peptides, named microginins T1 (1) and T2 (2), micropeptins T1 (3) and T2 (4) and anabaenopeptin T (5), were isolated from cyanobacterial water bloom materials of lake Teganuma (Japan), collected in 1994, 1995 and 1997. Their structures were determined by two-dimensional 1H-1H and 1H-13C NMR correlation experiments and confirmed by mass spectral and amino acid analyses. Their stereochemistries were deduced by spectral and chemical studies. The peptides showed a unique pattern of inhibition when tested in assays for trypsin, plasmin, chymotrypsin, leucine aminopeptidase, carboxypeptidase A and angiotensin-converting enzyme. Each peptide inhibited at least one and sometimes two proteases with characteristic IC50 values