Well, here is the statement from the 5D II White Paper: "... the weather and dust seals have been improved around the battery compartments and memory card doors, and increased precision in the alignment of the magnesium alloy external cover seams and in the optimal design of parts and structures contribute to the cameras’ dust and water resistance. Internal gaskets and sealing materials are used extensively at the cameras’ buttons, tripod sockets, and surrounding the LCDs. As a result, the EOS 5D Mark II now has dust and water resistance that is almost equal to that of the EOS-1N—Canon’s top-of-the-line professional 35mm SLR for most of the 1990’s."