20-hydroxy LTB4 is a metabolite of LTB4 in human neutrophils. In human leukocytes, LTB4 is inactivated by the enzyme LTB4 20-hydroxylase. 20-hydroxy LTB4 is not only much less active (~5%) compared to LTB4 in causing degranulation of PMNL, but actually inhibits LTB4-induced degranulation of human neutrophils (Ki = 13.3 nM). However, 20-hydroxy LTB4 is as active as LTB4 in contracting parenchymal strips from guinea pig lung. 20-hydroxy LTB4 retains considerable ligand binding affinity at the BLT2 receptor, but does not appear to function as an agonist.