We report new estimates of transport rates for H2O and Cl between the mantle and surface reservoirs. Our estimates take into consideration alteration of oceanic crust, especially that of plutonic rocks, and possible subduction of sediments. The effect of (hydrothermal) alteration on the Cl budget seems to be negligible, but the effect on the H2O budget is significant. Altered oceanic crust (excluding sediments) contains about 10 times as much H2O as the unaltered crust, and its subduction may result in a net transport of H2O to the upper mantle in subduction zones. However, the rate of expulsion of H2O from the mantle by subduction-zone magmatism is comparable to the amount released by ridge magmatism, and is only about 10% of the amount subducted. Therefore, about 90% of the subducted H2O must be returned to the mantle or returned to the crust by other processes. In addition, subduction of oceanic sediments to mantle depths will result in 1. (1) a further increase in the return rate of H2O to the mantle reservoir, 2. (2) possible net transfer of Cl to the mantle, depending on the rate of pore water expulsion.