Kinetic studies have been made of the interaction of carbon monoxide with the {100} and the stepped {320} planes of tungsten. No marked influence of the steps on kinetic processes or on the nature of the chemisorbed overlayer was observed. At 300 K, the saturation coverage on both planes is ≈ 10 × 10¹⁴ molecules cm^–2, although the initial sticking probability, s_o, is higher (0.9) on W{320} than on W{110}(0.46). Desorption spectra for both planes are similar, showing, after 300 K adsorption, α_{1, 2}, β₁ and β₂ peaks. Evidence is produced for the existence of an α₃ state on both planes, which can be increased in population by adsorption at temperatures above 500 K. Conversion from the “virgin” CO state formed at 85 K to β-CO is characterised by secondary electron emission studies; the activation energy for this process on W{110} is ≈ 77 kJ mol^–1, compared with an estimated desorption energy of ≈ 110 kJ mol^–1. Very little difference could be found between the “virgin” and the α_1,2 state. Reasons are discussed for the observed pseudo-first-order desorption behaviour in the dissociatively bound β states on both crystal planes.