The catalysed decomposition of N₂O in the range 830–1000 K and 0.05–1.0 Torr (1 Torr ≈ 133 Pa) has been examined on Pd single-crystal surfaces and polycrystalline wires and compared with earlier work. The relative reaction velocities at 1000 K and 0.2 Torr are as follows: 0.01 cm diameter wire, 21; 0.025 cm diameter wire, 10.9; (610) plane, 2.2; (100) plane (thin disc), 1.8; (110) plane, 1.8; (100) plane (normal thickness disc), 1.7; and (111) plane, 1.0. Kinetic equations describing the first-order inhibition in oxygen pressure derived earlier by Eley and Knights for O₂ chemisorbed as molecules have been rederived in terms of an adsorption–desorption reaction between chemisorbed oxygen atoms and ‘transitional’ or ‘subsurface’ oxygen atoms. The apparent activation energies for Pd (and for the earlier PdAu wires) have been discussed in terms of this mechanism. From the above, ‘stepsites’ on (610) furnish sites ca. 2.7 times more active than terrace sites on (100), while grain boundaries may well be responsible for the more active sites on the Pd wires. By implication, since pure Au is known to show negligible chemisorption of O₂ at 1000 K, it seems possible that grain boundaries furnish the only active sites for N₂O decomposition on that metal.