The U.S. Nuclear Regulatory Commission (NRC) requires utilities to determine the response of a pressurized water reactor (PWR) to a steam generator tube rupture (SGTR) as part of the safety analysis for the plant. The SGTR analysis includes assumptions regarding the presence of fission product iodine in the reactor coolant resulting from iodine spikes. To get a better understanding of iodine spiking, reactor trip and associated radiochemistry data were collected from 26 PWRs. These data were compared against validation criteria to determine their applicability to an investigation of the magnitude of an iodine spike following a reactor trip. The applicable data and the results of a statistical analysis are presented. Conclusions are made from this analysis of iodine spiking following reactor trips concerning the magnitude of a spike during an SGTR and compared with the NRC analysis criteria. The conclusion is then made that the iodine release rate expected during an SGTR, on the basis of the analysis of the data base, is much less (by a factor of 15 or more) than that specified by the NRC for analysis of this accident type.