The preparation of a tritiated radiotracer that was used in the radioimmunoassay of naringin (naringenin-7-O-alpha-rhamnosyl- (1-2)-beta-d-glucopyranoside) and which was synthesized by reduction of the carbonyl group of the flavanone is reported. The resulting assay has a detection limit of 0.5 picomole per 0.1 milliliter, is specific for the 7-neohesperidoside substitution on flavanones, and can measure naringin in crude extracts of plant tissues. This radioimmunoassay is compared with three other naringin immunoassays which use antibodies raised against two different haptens and different tracers labeled with (125)I or (3)H. The applicability of the methods to the quantification of naringin and other flavanone neohesperidosides in citrus tissue is discussed.