The combination of the relative rate method with the discharge fast flow/mass spectrometer technique (RR/DF/MS) has been developed to measure the rate constants for gas phase reactions involving OH radicals. The RR/DF/MS technique was used to measure the rate constant for reactions of the OH radical with n-octane (k(3)) and cyclohexane (k(5)) using 1,4-dioxane as a reference compound, and with n-decane (k(12)) using n-octane and 1,4-dioxane as reference compounds. At 298 K, these rate constants were determined to be k(3) = (8.88 +/- 0.31) x 10(-12), k(5) = (6.95 +/- 0.20) x 10(-12), and k(12) = (1.38 +/- 0.08) x 10(-11) cm(3) molecule(-1) s(-1), respectively, which are in very good agreement with those measured using different techniques. The features of the RR/DF/MS technique are discussed. (C) 2003 Elsevier B.V. All rights reserved.