An on-line radioiodine monitoring system designed to operate under nuclear accident conditions is tested at the hot cell laboratory of a radiopharmaceutical production facility. The purpose of the work is to demonstrate that the patented Pennsylvania State University radioiodine monitor, using stabilized NaI(Tl + 241Am) detectors, can generate information about concentration of airborne radioiodine in real time. In the test of continuous iodine monitoring, the real-time 132I activities agree with those obtained by a high-purity germanium detector within a factor of ∼4. From the simultaneous operation of two monitors, one at the inlet and one at the outlet of the hot cell filter bank, the hot cell filter bank efficiency for the removal of airborne radioiodine is estimated to be at least 99.88%.