New antibiotic Y1-HU3 has the following characteristics: (a) mol. wt. 469; (b) m.pt. 180-190oC, pale yellow crystals; (c) UV spectrum has two maxima at 312 nm and 300 nm (in chloroform); (d) soluble in methanol, chloroform; (e) insol. in n-hexane. The IR, 1H NMR and 13C NMR spectra are given. Antiobiotic Y1-HU3 is obtd. by culture of Pseudomonas species Y1-Hu (FERM-BP 1610). In an example Pseudomonas sp. Y1-HU is cultured in potato dextrose medium at pH and 28 deg. C for four days. The cell bodies are sepd. and the culture filtrate extracted with chloroform. The extract is concd. and chromatographed on silica gel (Wakogel C-200) using chloroform as eluent. The produce is dissolved in chloroform/methanol and hexane added to give antibiotic Y1-HU (10 mg from 1 litre culutre).