Plasma membrane sheets from Xenopus oocytes have been isolated for use in FRET measurements. This system has the following advantages: 1) fluorescent recordings from a large surface area to maximize the signal to noise ratio; 2) reduction in background fluorescence from proteins retained in intracellular compartments; 3) access to the cytoplasmic surface of the plasma membrane for rapid solution changes. To demonstrate the utility of this approach we have examined a previously published FRET based Ca²⁺ sensor- namely the Cameleon-PM. This construct targets to the plasma membrane and upon various Ca²⁺ additions to the cytoplasmic face of the membrane shows ratiometric FRET changes. From the ratiometric changes recorded, an apparent Ca²⁺ affinity of 1.65 µM was determined. Thus, preparation of Xenopus oocyte plasma membrane sheets and FRET measurements, demonstrates all three of the advantages outlined above.