[en] The yttrium yields, in the determination of Sr-90 in environmental samples as obtained by several laboratories were found to be greater than 100%. To decrease this gravimetric error, a barium sulphate precipitation step followed the strontium yttrium separation, to scavenge any traces of strontium or calcium. The yttrium recovery was decreased to values lower than 100% as expected. Consequently, an increase of 5-8% in the counting efficiency of Y-90 was obtained while that of Sr-90 remained unchanged. Another bias has been met in comparing the gravimetric to the radiometric recoveries, called the recovery bias and is equal to Grav. Rec.-Rad.Rec. x 100/ Rad. Rec. For treating this recovery bias, two different procedures were used including the use of different chemical separation steps and different strontium carrier concentrations. These are the American Society for Testing and Materials (ASTM) and the Yankee Atomic Environmental Lab.(YAEL) procedures. It was found that the use of YAEL procedure with the higher strontium carrier concentration (50 mg/ml) of the ASTM leads to an acceptable recovery bias.2 fig.,1 tab