20-carboxy LTB4 is a metabolite of LTB4 in human neutrophils. In human leukocytes, LTB4 is inactivated by the enzyme LTB4 20-hydroxylase. The resulting 20-hydroxy LTB4 is further oxidized to 20-carboxy LTB4.{377} LTB4 metabolism in isolated rat hepatocytes also results in production of 20-carboxy LTB4 along with other ω-oxidation products.{1032} The biological activity of 20-carboxy LTB4 is only about 2.6% compared to that of LTB4 in causing PMNL degranulation.{399}