Microginins 299-A (1 and -B (2) have been iscdated from the cyanobacterium MicroQ,stis aeruginosa (NIES-299). Their structures were determined by tw(~-dimensional I H-iH and iH-i'~c NMR correlation experimems and confirmed by mass spectral and amino acid analyses, Their absolute stereochemistries were deduced by a combination of spectral and chemical studies. I and 2 inhibited leucine aminopeptidase with ICso's of 4.6 and 6.5 lag/mE respectively. • ~ 1997 Elsevier Science Ltd.