In this paper, an experimental study on the heat transfer characteristics of two-phase flow boiling of alternative zeotropic refrigerant mixtures to R-502, on air/refrigerant horizontal enhanced surface tubing is presented. The new alternatives considered in this study are: R-507, R-404A, R-407B, and R-408A. It was evident from the experimental data that R-502 has the lowest heat transfer rate compared to the other blends in the range investigated. Furthermore, it was also quite evident from these data that R-407B has the highest pressure among the blends under investigation. However, at a Reynolds number less than 3.6 x 10(4), it appears from the data that R-404A has the lowest pressure drop compared to other refrigerants under investigation.