Chelation therapy is sometimes used after potential exposures to plutonium to increase urinary excretion of the radionuclide to improve the accuracy of bioassay measurements. The purpose of this report is to describe the enhancement of urinary excretion of plutonium during and after the administration of the trisodium salt of calcium diethylenetriaminepentaacetate (Ca-DTPA) daily for 3 d to a group of male and female plutonium workers from the Mayak Production Association in Ozyorsk, Russia. One-hundred and two cases (18 females and 84 males) were selected where urinary contents of plutonium, prior to chelation, exceeded the detection threshold. Daily urine collections were obtained during the 3 d of Ca-DTPA treatments. In addition, 58 of these cases had urine bioassays at 1-45 d after chelation. The daily enhancement over baseline values excretion of plutonium was found to be 50.4×/1.4 (geometric mean and geometric standard deviation); 58.9×/1.2; 72.9×/1.4 in the first, second and third days of Ca-DTPA administration. The mean enhancement for the 3-d period was 60.1×/1.7. The rate of plutonium excretion from 1 to 45 d after chelation decreased with a half-period of 3.9 d and the chelation enhancement factor (Кenh-i) is described by the function Кenh-i = (0.79 ± 0.24) + (42.9 ± 1.2) × e-(0.18 ± 0.01) × day.