The thermal desorption of carbon monoxide from alumina-supported platinum has been studied by monitoring of the infrared spectrum of adsorbed CO as the temperature is increased. For the 0.5, 1, 2, and 10 wt% Pt samples studied, the areas of the peaks in the linear region increased with temperature until 100 °C, whereupon they decreased steadily, reaching zero at about 400 °C. The rate of disappearance of linearly adsorbed CO had two maxima, one at about 150 °C and the other at about 250 °C. The 0.5, 1, and 2% samples, which were fully dispersed, all displayed a peak at 2060 cm −1, with a shoulder at about 2078 cm −1. The 10% sample, which was 75% dispersed, had its main peak at 2083 cm −1 with a shoulder at 2069 cm −1. For all samples, these peaks shifted to lower frequency as the temperature increased. The 2083 cm −1 peak is attributed to CO linearly adsorbed on Pt crystal faces, whereas the 2060 cm −1 peak is attributed to CO adsorbed by Pt particles that do not have extended crystal faces.