Abstract A rapid, precise and accurate radioimmunoassay for the measurement of digoxin has been developed. The method employs a column of immobilized antibody which acts as both reaction chamber and separation device. In a two-step procedure, a diluted specimen and radiolabeled digoxin derivative are added, in turn, to the column and allowed to incubate for 30 min each. A buffer wash separates the antibody bound from free drug. The sensitivity of the assay is about 7.5 pg, while the average intra- and inter-assay coefficients of variation are 10 and 12%, respectively. The assay exhibited satisfactory recovery and parallelism, and correlated well with a reference procedure.