  The well known Sunyaev-Zel'dovich (SZ) effect is reexamined using a Doppler
shift type mechanism arising from the scattering of photons by electrons in an
optically thin gas. The results are in excellent agreement with the
observational data as well as with the results obtained using the diffusive
pictures. A comparison of the results here obtained with other approaches is
thoroughly discussed, as well as some important extensions of this method to
other aspects of the SZ effect
