The development of a competitive solid-phase immunoassay for digoxin making use of the acridinium chemiluminescence system is described. Two different instrumental approaches are compared. One is based on a continuous flow system using a peristaltic flow injection analysis pump; the other uses a new sequential injection technique. In both systems a flow cell, consisting of transparent PTFE tubing packed with immobilized antibodies, acts as an immunoreactor. The entire assay, including both the immunoreaction and the chemiluminescence reaction, takes place in this immunoreactor cell. Compared with the flow injection technique, the sequential injection mode showed higher precision, ranging from 2.16 to 5.5% RSD depending on concentration. The total assay time, including regeneration, is less than 8 min with the sequential injection technique. The detection limit for both techniques is in the low femtomole range.