The next experiment was performed to determine the effect of plant materials on reactive oxygen species (ROS)
production. The NBT dye reduction test was used to determine the superoxide radical production by measuring
PMNLs containing formazan deposit (Fig. 1). The fresh human PMNLs were exposed to a stimulant alone or with plant
extracts. The results showed that G. mangostana could significantly reduce ROS production with the inhibitory ratio at
77.80±1.28%. H. cordata and S. siamea also showed high ability to inhibit ROS production. E. odoratum and S. alata
showed some inhibitory activity whereas A. paniculata and B. lupulina had insignificant activity on the generation of
ROS.