The two-phase frictional characteristics of refrigerants R-22, R-407C, and R-410A in small diameter tubes are reported. Tests were performed in 3, 5, 7, and 9 mm diameter tubes. The range of mass velocities ranges from 50 to 700 kg m(-2) s(-1). It is found that for a fixed mass flux, saturation temperature and quality, the pressure drops for R-22 are higher than those of R-407C and R-410A. The predictive ability of existing correlations such as the Friedel correlation, the homogeneous model, and the Souza and Pimenta correlation are comparable at a mean deviation of 30 similar to 35%. However, the predictive ability of the Chisholm correlation is quite poor. Based on the test results of this study and other investigations, modifications to the homogeneous model and the Chishom correlation are made; the relevant mean deviations of the modified correlations are around 17 similar to 18%.