The biotransformation of the phytoanticipins 2-benzoxazolinone (BOA) and 2-hydroxy-1,4-benzoxazin-3-one (HBOA) by four endophytic fungi isolated from Aphelandra tetragona was studied. Using high-performance liquid chromatography-mass spectrometry, several new products of acylation, oxidation, reduction, hydrolysis, and nitration were identified. Fusarium sambucinum detoxified BOA and HBOA to N-(2-hydroxyphenyl)malonamic acid. Plectosporium tabacinum, Gliocladium cibotii, and Chaetosphaeria sp. transformed HBOA to 2-hydroxy-N-(2-hydroxyphenyl)acetamide, N-(2-hydroxyphenyl)acetamide, N-(2-hydroxy-5-nitrophenyl)acetamide, N-(2-hydroxy-3-nitrophenyl)acetamide, 2-amino-3H-phenoxazin-3-one, 2-acetylamino-3H-phenoxazin-3-one, and 2-(N-hydroxy)acetylamino-3H-phenoxazin-3-one. BOA was not degraded by these three fungal isolates. Using 2-hydroxy-N-(2-hydroxyphenyl)[(13)C(2)]acetamide, it was shown that the metabolic pathway for HBOA and BOA degradation leads to o-aminophenol as a key intermediate.