The kinetics of the self-reaction of ethyl radicals was studied by laser photolysis/photoionization mass spectroscopy. Overall rate constants were obtained in direct real-time experiments in the temperature region 301-800 K and at bath gas (mostly helium, balance radical precursors) densities of (3.00-12.0) x 10(16) molecules cm(-3). Ethyl radicals were produced in well-characterized concentrations by a combination of the 193-nm photolysis of oxalyl chloride ((CClO)(2)) with the subsequent fast reaction of Cl atoms with ethane. The observed overall C2H5 + C2H5 rate constants demonstrate a negative temperature dependence. Master equation modeling of collisional effects indicates that the reaction is in the high-pressure limit under all experimental conditions except for those used at the highest temperature, 800 K, where a minor falloff correction (8%) was applied to obtain the high-pressure-limit rate constant value. The following expression for the high-pressure-limit rate constant of reaction I was obtained: k(l)(infinity) = (2.29 x 10(-6)) T-1.66 exp(-552 K/T) cm(3) molecule(-1) s(-1). The disproportionation to recombination branching ratio was determined at 297 and 400 K; the results are in agreement with the well-established value of 0.14.