Bacteria isolated from the skin of the pufferfish Fugu poecilonotus were screened for tetrodotoxin production. Tetrodotoxin and its derivatives were detected by HPLC analyses in broth cultures of a Pseudomonas sp. Upon alkali treatment the compounds yielded, as do tetrodotoxin and its derivatives, 2-amino-6-hydroxymethyl-8-hydroxyquinazoline, the identity of which was confirmed, after methylation or trimethylsilylation, by HPLC, mass spectrometry and gas chromatography - mass spectrometry.