Phosphotriesterase (PTE) activity from Flavobacterium sp. was investigated in the presence of either two types of nonionic, 14 types of anionic, one type of cationic, or teo types of amphoteric detergents. The highest PTE activity toward diethyl 4-nitrophenyl phosphate (Paraoxon) was observed in the presence of 0.01% sodium carboxyl polyoxyethylene tridecylether, which was 1.7 fold higher than that without detergent. Lyophilized PTE prepared in the presence of 60 mM trehalose retained about 75% of initial preparation after 25 days of storage at 25 degrees C, which was 3 fold higher residual activity of the sample prepared in the absence of trehalose.