The present study has been carried out to investigate the effect of sodium benzoate, potassium sorbate, butyl p-hydroxybenzoate and sodium dehydroacetate, preservatives used as food additives in Japan, at ADI levels on cell functions both in vitro and ex vivo. Washed platelets from rabbit were used and the magnitude of A-23187 and thromobin induced TXB₂ synthesis in the presence or absence of preservatives were used as a marker of the effects. Among preservatives used, butyl p-hydroxybenzoate had strong inhibitory effects on both agonists induced TXB₂ synthesis in vitro, and significant inhibitory effect on thrombin induced one ex vivo. In contrast, sodium bensoate had relatively weak inhibitory effects on thrombin induced TXB₂ synthesis in vitro, but it inhibited thrombin induced one very significantly ex vivo. These results suggest that continuous intake of butyl p-hydroxybenzoate and especially sodium benzoate at ADI level might affect platelet functions.