The plutonium rapid response in vitro bioassay method described here was designed to determine 238Pu, 239Pu, and 240Pu concentration in urine samples from workers with potential internal contamination. Results provide quick and actionable information about the level of contamination necessary to assist making further medical decisions, including chelation therapy. The radiochemical procedure can be performed within approximately 48 h, including sample preparation, measurement(s) by alpha spectrometry and/or inductively coupled plasma mass spectrometry (ICP-MS), and data evaluation. [ABSTRACT FROM AUTHOR]