Abstract: The absorption cross section of Reissner-Nordström black holes is computed for massless particles of spins 0, 1, and 2. We apply numerical methods in order to obtain the absorption cross section for arbitrary values of the wave frequency since general solutions are very difficult to be found analytically. We match these results with the analytical ones that are valid only in the low- and high-frequency regimes. For the massless scalar field case in the low-frequency limit, the absorption cross section equals the black hole area, that is a general result valid for any asymptotically flat stationary black hole. On the electromagnetic and gravitational cases, the absorption cross sections are obtained taking into account the interconversion of these two kind of waves. The conversion of waves leads to a very interesting result: the (total) absorption cross sections for both electromagnetic and gravitational cases are the same for extremely charged black holes. This result is showed analytically and numerically.