Abstract: A solid-phase reactor was prepared from PbO2 entrapped by polymerization of unsaturated esters in a polyester resin. The powdered material of particle size 200-250 µm was introduced into a 1.5 mm i.d. PTFE tube and placed in a FIA continuous-flow manifold. An aqueous solution of ondansetron in H2SO4 medium was injected into a carrier stream of water and passed through the reactor at a flow rate of 5.4 ml/min. The released Pb(II) was monitored by AAS at 217 nm. The calibration graph was linear in the range 0.5-20 µg/ml of ondansetron at room temperature and, for a sample volume of 405 µL, the throughput was 338 samples/h. The RSD for 10 µg/ml of analyte at room temperature and 80°C were 2% (n = 29) and 1.8% (n = 35), respectively. The between-day reproducibility had a RSD of 2.1% and foreign compounds did not interfere. The method was applied to the analysis of tablets.