Peroxy radical (RO₂) chemistry is central to the oxidation of volatile organic carbon in the troposphere. Kinetic studies of their reactions are rendered difficult by competing self- and cross-reactions, especially the poorly characterized secondary production of HO₂ from RO₂ self-reactions.  In this experiment C₂H₅O₂ and HO₂, were generated by pulsed laser photolysis and monitored simultaneously and independently using UV absorption and wavelength modulation near-IR spectroscopies. Their self- and cross-reactions were investigated over a wide range of relative concentrations, at T=221-296 K and p=50-200 Torr. The Arrhenius expression for the cross reaction rate constant is k₂(T) = (5.58±1.80) x 10^-13 exp(672±74) cm³ molecules^-1 s^-1, and is in general agreement with previous studies.  The high sensitivity for HO₂ detection led to the first direct measurement of the branching fraction to the radical channel in the C₂H₅O₂ self-reaction. The result, α = 0.24±0.05 is less than half that reported in the literature.