Spatial concentration and temperature profiles of the CH radical in a hot-filament chemical vapor deposition reactor are measured by cavity ring-down spectroscopy. The CH concentration is found to be on the order of 10(11) molecules/cm(3). The spatial distribution indicates that CH formation primarily occurs at or very near the filament. At a distance of 2 mm from the filament the [H]/[H-2] ratio is determined to be 0.011 +/- 0.003.