The absolute rate constants for the gas-phase H-atom abstraction by hydroxyl radicals from cyclohexane and ethane have been determined at room temperature. OH radicals were produced by pulse radiolysis of an H₂O-Ar mixture, and the decay of OH was followed by monitoring the transient light absorption around 309 nm. The rate constants were found to be k = (5.24±0.36) × 10^-12 and (2.98±0.21) × 10^-13 cm³ molecule^-1 s^-1 for cyclohexane and ethane, res- pectively. These results are compared with literature data.