We report the fabrication and characterization of a biologically sensitive field-effect transistor (Bio-FET) using a nanocrystalline diamond thin film. Biomolecular recognition capability was provided by linking human immunoglobulin G (IgG) to the diamond surface. Electrical measurements reveal behavior characteristic of field-effect transistors. The biomolecular recognition and specificity characteristics were tested using the two antibodies anti IgM and anti-IgG. Electrical measurements show that the Bio-FET device made on an IgG-modified diamond exhibits a response specific to the anti-IgG antibody. Our results demonstrate the ability to fabricate a bio-FET device using a biologically modified diamond thin film. (C) 2004 American Institute of Physics.