The recommended method for controlling the radiochemical purity (RCP) of 99Tcm-labelled tetrofosmin is thin-layer chromatography (TLC) with silica gel as the stationary phase and acetone:dichloromethane (35:65, v/v) as the mobile phase. However, this test is time-consuming and uses a toxic substance. We propose an alternative method to control RCP, based on a solid-phase extraction method (SPE) using a Sep Pak C18 cartridge. We used both methods to analyse 35 samples and to determine the percentages of colloid, radiopharmaceutical and free 99Tcm-pertechnetate. Normal labelling processes were modified to obtain a wide range of values. The range of RCP values obtained was 63.4-96.5% (median = 93.8%) by the standard TLC method and 70.1-96.4% (median = 94.1%) by the SPE method. A significant difference was observed only for the percentage of free 99Tcm-pertechnetate (P < 0.05). The agreement between the two methods, using 90% RCP as the limit, gave a kappa index = +1 (P < 0.001), indicating total agreement between them. The proposed method is useful to control RCP because it yields results that are in good agreement with those of the standard method, and because it is safer and less time-consuming.