We investigated developmental changes in the activity of cytosolic phospholipase A2 (cPLA2) in the rat brain. When the cytosolic fractions from rat brain of various ages were examined by gel filtration chromatography, cPLA2 activity was detected at about 100 kDa in all developmental stages. However, the magnitude of cPLA2 activity differed significantly. The cPLA2 activity was highest in the brain of day-12 embryo, gradually decreased toward birth, and retained a constant level into adulthood. This result suggests that cPLA2 plays an important role in the early development of the nervous system.