An indirect atomic absorption spectrometric assay for epoxide hydrolase was reported. The enzymatic product 1,2-diol was oxidized by an excess of potassium periodate, and the unconsumed periodate was preferrentially precipitated by lead periodate. The precipitate was acid digested followed by atomic absorption determination of lead in the resulting solution. Trans-stilbene oxide (TSO) induced rabbit and tilapia epoxide hydrolase activities by 350% and 210% at the 490 mg TSO/kg treatment while Aroclor 1254(AR) only slightly increased their activities at the 200 mg AR/kg treatment. The 1,2-epoxy-3,3,3-trichloropropane (TCPO) at 0.1 mM completely inhibited tilapia (control) and rabbit (490 mg TSO/kg) epoxide hydrolase activities.