Chemical vapor transport of platinum (Pt) and rhodium (Rh) has been studied in closed ampoules using a 900-800 degrees C over 100 mm gradient for periods of 123-365 days. The ability of O-2, air, and H2O to act as transport agents has been evaluated, control experiments have been performed with vacuum, N-2, and Ar, and surveying experiments have been made with NH3\, NO, and H,. Transport of Pt and Rh occurs in the presence of oxygen (regardless of source), manifested as single-crystal growth at the colder end of the ampoules. PtO2 and RhO2 were identified as vapor molecules by in situ mass spectrometric monitoring. A small transport of Rh is indicated for H2O as agent, whereas no transport is observed in N-2, H-2, NH3, and Ar atmospheres. (c) 2005 Elsevier B.V. All rights reserved.