The occurrence of alanine dehydrogenase (AlaDH), glutamate dehydrogenase (GDH), and 2-ketoglutarate:glutamine amidotransferase (GGAT), has been surveyed in a number of blue-green algae. Among nine unicellular strains grown with nitrate, and belonging to five of the major typological groups, AlaDH was present in seven, and GDI-I in all eight that were assayed. In ten filamentous strains grown with nitrate, and belonging to the three nonheterocyst-forming and four hetcrocyst-f0rming groups, AlaDH was present in six, but both AlaDH and GDH were present in only one strain. In those strains which could be grown with N2 as sole nitrogen source, levels of GDH were generally lower, and AlaDH higher in cells fixing N 2 than in those growing with nitrate. GGAT was undetectable in Negrown cells. Two unicellular and three filamentous strains were tested for their ability to use T.-alanine, n-glutamate, L-glutamine, and n-asparagine as sole sources of nitrogen. Of these, L-asparagine was utilized most effectively. There was little difference in levels of GDH in cells grown with nitrate or with L-asparagine, while the levels of AlaDtt were slightly lower in cells grown with L-asparagine.