The present invention relates to an isolated leukotriene A.sub.4 (LTA.sub.4) hydrolase, which LTA.sub.4 hydrolase is present in its naturally occurring three dimensional form. It is the first three-dimensional structure of any protein component of the leukotriene cascade and enables a description of the structural basis and molecular mechanisms for the two catalytic activities of LTA.sub.4 hydrolase. Further, the invention also relates to LTA.sub.4 hydrolase complexed with an inhibitor. The structural information provided by the present invention will make possible rational design of enzyme inhibitors, which may be developed into clinically useful anti-inflammatory drugs.