This work presents a flexible and light air-breathing hybrid microfluidic fuel cell (H mu FC) operated under biological conditions. A mixture of glucose oxidase, glutaraldehyde, multi-walled carbon nanotubes and vulcan carbon (G0x/VC-MWCNT-GA) was used as the bioanode. Meanwhile, integrating an air-exposed electrode (Pt/C) as the cathode enabled direct oxygen delivery from air. The microfluidic fuel cell performance was evaluated using glucose obtained from three different sources as the fuel: 5 mM glucose in phosphate buffer, human serum and human blood. For the last fuel, an open circuit voltage and maximum power density of 0.52 V and 0.20 mW cm(-2) (at 0.38 V) were obtained respectively; meanwhile the maximum current density was 1.1 mA cm(-2). Furthermore, the stability of the device was measured in terms of recovery after several polarization curves, showing excellent results. Although this air-breathing H mu FC requires technological improvements before being tested in a biomedical device, it represents the best performance to date for a microfluidic fuel cell using human blood as glucose source. (c) 2015 Elsevier B.V. All rights reserved.