The construction and performance of a combined reaction cell and sample exchange lock for studies of surface reactions at pressures up to a few atmospheres is described. In combination with a specially designed sample holder this construction allows simple and rapid transfer of the sample betwen the ultrahigh vacuum system and the reaction cell. The reaction cell is a self‐contained unit that can be mounted on, e.g., a 2 3/4 ‐in. Con‐Flat flange (or any other vacuum port with an I.D.≥38 mm). The sample holder can be mounted on any commerical sample manipulator. In both the high‐ and low‐pressure positions the sample can be heated and cooled. Results are presented for the times involved in moving the sample from high‐ to low‐pressure environments, pump‐out times, etc. The use of this equipment in studies of the catalytic activity of Pt for the H2oxidation is briefly described.