A cryogenically cooled sample holder and support assembly has been constructed for surface x-ray diffraction studies in ultrahigh vacuum. The design combines ease of sample replacementin situwith good mechanical stability and temperature control. This is achieved by locating a rectangular pin on the sample holder in a collet which can be closed from outside the vacuum chamber. Samples up to 10 mm square can be held at a constant temperature between 40 and 1300 K. ©1997 American Institute of Physics.