1. Microsomal fractions from Trypanosoma cruzi epimastigotes catalyze the hydration of styrene oxide to styrene glycol. The activity is linear up to 45 min of incubation, is proportional to microsomal protein concentration within certain range, and has an optimum pH of 8.5. 2. Double-reciprocal plots indicate a Km value of 5.3 . 10(-4) M for styrene oxide and a V of 29.6 pmol of styrene glycol formed/min per mg protein at 37 degrees C. 4-Chlorophenyl-2,3-epoxypropyl either (Ki = 2.08 . 10(-4) M) and juvenile hormone I (Ki = 2.7 . 10(-4) M) are competitive inhibitors; whereas, 1-chloro-2,3-epoxypropane is a non-competitive inhibitor. The enzyme is induced about three-fold by 5 mM phenobarbital in the growth medium. 3. The epoxide hydrase is not activated by detergents but rather inhibited by concentrations of Tween-80 and Lubrol as low as 0.025%. 4. Experiments with intact cells indicate that about 3% of [8-14C]styrene oxide penetrates after 90 min of incubation; whereas, over 30% of juvenile hormone I is found intracellularly after the same incubation period. Intracellular styrene oxide is hydrated to styrene glycol to a significant extent and the in vivo hydration is increased by pretreatment with phenobarbital and inhibited upon the addition of 4-chlorophenyl-2,3-epoxypropyl ether. Only a small amount of the intracellular juvenile hormone I is recovered as the corresponding diol ester.