A first measurement of the radiative contribution to deep inelastic electron-proton scattering has been performed with the ZEUS detector at HERA. Results show consistency with predictions made by the HERACLES Monte Carlo program. New calibration and simulation of the far luminosity measurement system, including a photon calorimeter and two aerogel Cherenkov detectors, have been implemented. Both calibration and simulation were applied to tag photons produced in the initial state radiative process. These tagged events were used to perform measurements of the deep inelastic ep scattering reduced cross section down to momentum transfer squared, Q2 = 3.0 GeV2, a region normally inaccessible to ZEUS. A determination of the radiative contribution to deep inelastic scattering has aided in the measurement of the structure functions F2 and FL, which were simultaneously extracted in the kinematic region 8.0 GeV2