A Bacillus licheniformis strain, I89, isolated from a hot spring environment in the Azores, Portugal, strongly inhibited growth of Gram-positive bacteria. It produced a peptide antibiotic at 50degreesC. The antibiotic was purified and biochemically characterized. It was highly resistant to several proteolytic enzymes. Additionally, it retained its antimicrobial activity after incubation at pH values between 3.5 and 8; it was thermostable, retaining about 85% and 20% of its activity after 6 h at 50degreesC and 100degreesC, respectively. Its molecular mass determined by mass spectrometry was 3249.7 Da.