This study was aimed to investigate the effect of essential oil on human neutrophil (HN) functions. The neutrophils were isolated on percoll gradients, counted, and tested for viability using the trypan blue exclusion method. The chemotactic response was based on a multiple blind well assay system. The control movement and chemotactic response of neutrophils to 0.1 microM fMLP were reduced at a dose-dependent manner. The essential oil significantly inhibited neutrophil chemotaxis from 0.05 to 0.5 mg mL(-1). The inhibitory concentrations (IC(50)) showing 50% inhibition to induced neutrophil chemotaxis, and control movement were 0.08 and 0.07 mg mL(-1), respectively. The human neutrophil elastase secretion was inhibited by essential oil at a concentration dependent manner from 0.5 to 2.5 mg mL(-1). The components of essential oil are potent inhibitors for polymorpho nuclear leukocytes functions. The observed inhibition of neutrophil functions occurred via intracellular pathway. Active serine protease could be essential for neutrophil responding process and/or signal transduction pathways.