The adsorption and electrooxidation of CO at a Ru(0001) electrode in perchloric acid solution have been investigated as a function of temperature, potential and time using in situ FTIR spectroscopy. This builds upon and extends previous work on the same system carried out at room temperature. As was observed at room temperature, both linear (COL) and 3-fold-hollow (COH) binding CO adsorbates (bands at 2000-2045 cm(-1) and 1768-1805 cm(-1), respectively) were detected on the Ru(0001) electrode at 10 degreesC and 50 degreesC. However, the temperature of the Ru(0001) electrode had a significant effect upon the structure and behavior of the CO adlayer. At 10 OC, the in-situ FTIR data showed that the adsorbed CO species still remain in rather compact islands up to ca. 1100 mV vs Ag/AgCl as the CO oxidation reaction proceeds, with oxidation occurring only at the boundaries between the COad and active surface oxide/hydroxide domains. However, the IR data collected at 50 degreesC strongly suggest that the adsorbed CO species are present as relatively looser and weaker structures, which are more easily electro-oxidized. The temperature-, potential-, and coverage-dependent relaxation and compression of the COL adlayer at low coverages are also discussed.