In this paper, an experimental study on the heat transfer characteristics of two-phase flow boiling of alternative zeotropic refrigerant mixtures to R-22, on air/refrigerant horizontal enhanced surface tubing is presented. The new alternatives considered in this study are: R-507, R-404A, R-408A, R-407C, and R-410A. The experimental data showed that R-22 has the highest heat transfer rate compared to the other blends in the range investigated. Furthermore, it was also quite evident from these data that R-410A has the highest pressure among the blends under investigation for Reynolds number greater than 3.5 x 10(4). However, for Reynolds number less than 3.6 x 10(4), it appears from the data that R-22 has the highest pressure drop compared to other refrigerants under investigation.