Laser Induced Fluorescence (LIF) spectroscopy is used to study the temporal evolution of hydroxyl radical (OH) concentration in hydrogen-air repetitively pulsed nanosecond discharges at equivalence ratios of 0.5 and 1.0, and pressure and initial temperature of 40 Torr and 300 K, respectively, with the number of pulses in a 40 kHz burst varied between one and one thousand. Relative OH concentration data is put on an absolute scale by calibration with an atmospheric pressure near-adiabatic flat flame Hencken burner. Experimental time-resolved absolute OH radical concentrations as a function of time after initiation of a single discharge pulse, and as a function of number of pulses in the 40 kHz burst are found to agree well with predictions from a recently developed hydrogen-air plasma chemistry model which incorporates non-equilibrium plasma processes, low temperature H2–air chemistry, non-empirical scaling of nanosecond discharge pulse energy coupled to the plasma, and quasi-one-dimensional conduction heat transfer.