In order to obtain the optically specific antiserum used for radioimmunoassay of l-pentazocine a hapten-carrier conjugate was prepared from l-pentazocine 2'-carboxymethyl ether by coupling with bovine serum albumin employing the mixed anhydride technique. The antiserum elicited in the rabbit by immunization with this antigen was found to be highly specific to l-pentazocine.
