In the medium of EDTA-NaOH, nanogold strongly catalyzed the slow reaction between hydrazine (N2H4) and Cu(II) to form Cu particles, which exhibited a strong resonance scattering (RS) peak at 602 nm. The increased RS intensity at 602 nm (DeltaI(RS)) was linear to the nanogold concentration in the range of 0.008-2.64 nM, with a detection limit of 1.0 pM Au. The rate equation obtained by the initial rate procedure was V(Cu) = K(Cu)[C(Cu(II))](2)C(OH)(1)C(Au)(1)C(N2)H4(1), with an apparent activation energy of 38 kJ x mol(-1), and the catalytic reaction mechanism was also discussed. An immunonanogold-catalytic resonance scattering spectral (RSS) assay was established for detection of microalbumin (Malb), using 10 nm nanogold to label goat antihuman Malb to obtain an immunonanogold probe (AuMalb) for Malb. In pH 5.0 citric acid-Na2HPO4 buffer solution, the AuMalb aggregated nonspecifically. Upon addition of Malb, it reacted with the probe to form dispersive AuMalb-Malb immunocomplex in the solution. After centrifugation, the supernatant containing AuMalb-Malb was obtained, and exhibited a catalytic effect on the reaction of N2H4-Cu(II) to produce large Cu particles that resulted in the I(602 nm) increasing. The increased RS intensity at 602 nm (DeltaI(602 nm)) was linear to Malb concentration (C(Malb)) in the range of 0.4 to 460 pg x mL(-1), with the regression equation of DeltaI(602 nm) = 0.3713 C(Malb) + 7.2, correlation coefficient of 0.9981 and detection limit of 0.1 pg x mL(-1) Malb. The proposed method was applied to detect Malb in healthy human urine samples, with satisfactory results.