Hemoglobin (Hb) can take direct electron-transfer reactions after being entrapped in poly-3-hydroxybutyrate (PHB) film. A pair of well-defined, quasi-reversible cyclic voltammetric peaks is thus obtained at an Hb-PHB modified pyrolytic graphite electrode. The anodic and cathodic peaks are located at -224 and -284 mV for a pH 5.0 acetate buffer solution. Meanwhile, the peroxidase activity of the protein in the membrane has been greatly enhanced, with the apparent Michaelis-Menten constant calculated to be 1076 microM. According to the direct electron transfer property and enhanced peroxidase activity of Hb in the membrane, a Hb-PHB based hydrogen peroxide biosensor is prepared, with a linear range 6.0 x 10(-7) to 8.0 x 10(-4) M. The pathway of reductive dehalogenation of trichloroacetic acid is also discussed in detail. The highly reduced form of Hb produced in PHB film can be used to dechlorinate di- and monochloroacetic acid. The catalytic ability of Hb toward the reduction of nitric oxide has been investigated as well. Due to its biodegradability, low cost, chemical inertness, and especially its biocompatibility and non-toxicity, PHB would be a desirable film in the sensor field.