Absolute OH(A) and CH(A) concentrations were determined in low-pressure H-2-air and CH4-N2O flames, respectively, by measuring absolute chemiluminescence yields at 310 and 430 nm. From spatial profiles and intensities in these and other flames, we deduce that two reactions are responsible in each case, and derive rate constants for all. (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.