Disclosed are compounds of the formula (I): wherein R.sup.3, R.sup.4, R.sup.5, R.sup.9, and R.sup.10 are selected from the group consisting of H and groups or atoms other than H, and R.sup.6 and R.sup.8 are halo or hydrogen; X.sup.1, X.sup.2, and X.sup.3 are independently O or S; provided that R.sup.9 and R.sup.10 are not simultaneously H, when all of X.sup.1, X.sup.2, and X.sup.3 are O; and of the formula (II) wherein R.sup.11-R.sup.14 are selected from the group consisting of H and groups or atoms other than H; X.sup.4-X.sup.9 are independently O or S; n and m are 0 or 1 but m and n cannot be 0 simultaneously; R.sup.15-R.sup.24 can be H or any substituent so long as the compound of formula II upon hydrolysis provides a fluorescent compound. These compounds are useful as substrates with high specificity for organophosphatase particularly human paraoxonase and bacterial organophosphorus hydrolase. Also disclosed is a method for detecting and/or measuring the paraoxonase activity in a fluid comprising contacting the fluid with a fluorescent substrate and measuring the fluorescence of the fluorescent product formed. ##STR00001##