Accurate measurements of the speed of sound in the two refrigerants HFC227ea and HFC365mfc have been carried out by a double-path-length pulse-echo technique. The measured data for HFC227ea cover parts of the liquid and supercritical regions in the temperature range from (280 to 420) K with pressures up to 50 MPa, while those for HFC365mfc extend in the liquid region from (250 to 420) K with pressures to 100 MPa. The measurement uncertainties amount to 3 mK for temperature, 0.01 % for pressures below 10 MPa, 0.005 % for pressures between (10 and 100) MPa, 0.03 % for speed of sound in HFC227ea, and 0.04 % for speed of sound in HFC365mfc. Comparisons with literature data demonstrate the high accuracy of the measurements.