Silica-supported Pd clusters were characterized by in situ EXAFS spectroscopy. Clusters with an average nuclearity of six atoms were derived from either an inorganic or an organometallic precursor by reduction at 100-150 degrees C. Despite the small size of the clusters, EXAFS contributions from the metal-support interface were not detected. These clusters and larger ones formed by reduction at 320 degrees C absorb hydrogen on cooling in H-2 to 30 degrees C; the resultant interstitial hydride species decompose invacuo at 30 degrees C. Vacuum treatment at 300 degrees C removes chemisorbed H-2 yielding bare Pd clusters. In contrast to larger crystallites, the Pd clusters do not react with C2H4 at 150 degrees C to form interstitial carbide species.