Supported liquid extraction (SLE) techniques are relatively new compared to other sample preparation approaches such as solid phase extraction (SPE), liquid-liquid extraction (LLE) and protein precipitation (PPE). We investigated the use of SLE as an alternative to SPE for the liquid chromatography tandem mass spectrometry (LC-MS/MS) measurement of aldosterone. Samples (n = 83) were analysed by the routine method using SPE. The same samples were subsequently analysed using two different SLE 96-well plate devices (Thermo and Biotage) with methyl-tertiary butyl ether extraction. A direct comparison of the three extraction techniques on two different mass spectrometers was also performed. Both results using SLE plates gave excellent agreement with the results from the SPE analysis. The area counts obtained with the Biotage plates were considerably higher than those obtained using the Thermo plate. SLE is an acceptable alternative to SPE for the LC-MS/MS analysis of aldosterone. Using SLE reduces the time required for sample preparation.