Development of a radioimmunoassay for etorphine (preliminary communication).

A radioimmunoassay for etorphine has been developed using antibodies raised in a rabbit against an etorphine-3-hemisuccinate-bovine serum albumin conjugate. Using tritiated etorphine as the label, the antiserum could be used at a final dilution of 1:4 and had an avidity of 1.8 times 10-9 L.M.-1. The sensitivity of the assay was 0.88 plus or minus 0.04 ng etorphine per ml of serum and there was no cross-reactivity with any of the six opiate alkaloids examined over the range 0-100 ng/ml.