The behavior of a small-scale flow alkaline fuel cell (AFC) built-up for on-site production of HO2- using commercial gas-diffusion electrodes has been studied. It produces a spontaneous current due to the oxidation of H-2 to H2O at the H-2-diffusion anode and the reduction Of O-2 to HO2- at the O-2-diffusion cathode, while a fresh 1.0-6.0 mol dm(-3) KOH electrolyte at 15.0-45.0 degreesC is injected through it. Under circulation of HO2- + KOH solutions in open circuit, the flow AFC behaves as a two-electron reversible system. When it is shorted with an external load (R-ext), steady cell voltage-current density curves are found. The use Of O-2/N-2 mixtures to fed the cathode causes a loss of its performance, being required to supply pure O-2 to yield a maximum HO2-electrogeneration. The current density and HO2- productivity increase with raising OH- concentration, temperature and pressure Of O-2 fed. At R-ext = 0.10 Omega a current efficiency close to 100% is obtained, and current densities > 100 mA cm(-2) are achieved for 1.0 mol dm(-3) KOH at 45.0 degreesC and for higher KOH concentrations at 25.0 degreesC. The flow AFC can work under optimum conditions up to 6.0 mol dm(-3) KOH and 45.0 degreesC for possible industrial applications.