The delay time τ has been measured for the formation of the ·OH radical in igniting hydrogenoxygen mixtures diluted with argon (79–97%). The experiments have been carried out under incident shock wave conditions at temperatures of 900–3000 K, pressures of 0.5–2.5 atm, and H2/O2 ratios of 0.2–20. The dependence of τ on the pressure Ps of the stoichiometric part of the combustible mixture (2H2-O2) has been investigated for different mixture compositions. Under the above conditions, τ depends practically linearly on 1/Ps at Ps = 0.02−0.1 atm, irrespective of the mixture composition. This allows the measured τ data to be converted to one quantity, τPs. The temperature dependence of τPs in the Ps range from 0.02 to 0.1 atm is Arrhenius-like. For the hydrogen-rich mixtures (H2/O2 = 2–20), this dependence appears as τPs= 0.057 + 0.0256exp(7470/T) μs atm; for the lean mixtures (H2/O2 = 0.125–1), τPs = 0.021 + 0.0069exp(7470/T) μs atm. The length of the shock-heated gas plug in the incident shock wave poses limitations on the ignition delay time measurements at T < 900 K.