It has been discovered that a rapid dark reaction occurs on adding platinized TiO2 "photocatalyst" to liquid methanol before and/or during degassing resulting in large amounts of formaldehyde (mostly in the form of methoxymethanol) being present at the start of subsequent photolyses. The kinetics of this reaction has been studied in a magnetically stirred reactor over the temperature range 282-325 K, yielding an activation energy essentially equal to the value for diffusion of O-2 through CH3OH (1). The rate constants measured at t = 0 are only (2.4 +/- 0.7) x 10(-4) times theoretical diffusion-limited values, indicating that the rapid reaction only occurs at widely-spaced platinum-coated sites. Turnover numbers as large as 2200 per Ti atom(1.1 x 10(7) per active site) were measured after 27 h of reaction. Methyl formate, formic acid, and CO2 are observed as secondary reaction products, with some indication of higher hemiformals being formed as well.