Human tracheal epithelial cells were incubated with LTA4 and metabolic products were identified in extracted supernatants by high pressure liquid chromatography, ultraviolet spectroscopy, and gas chromatography-mass spectrometry. In the presence of epithelial cells, LTA4 was converted to LTB4, but not to LTC4 or LTD4. Maximum LTB4 was released at an LTA4 concentration of 3 microM and had occurred by 30 min. LTB4 release was increased in the presence of albumin, but was not affected by extracellular calcium or A23187. This LTA4 hydrolase activity had a slower time course and could not be clearly inactivated by repeated exposure to substrate as is the case for previously described LTA4 hydrolase enzymes. This hydrolase appears to have novel biochemical characteristics.