Based on the detection of agglutination of antibody- or antigen-bearing polymer by an immunoreaction using a piezoelectric quartz crystal, a piezoelectric immunoassay technique was developed for the determination of human serum albumin (HSA). The effect of experimental conditions including the polymer concentration, the antibody dilution ratio and the reaction temperature on the frequency response were investigated. The frequency responses were linearly correlated to the concentrations of HSA in the range of 112 – 878 μg ml−1. Other antigens present in serum did not interfere significantly with the determination of HSA. Analytical results of five clinical specimens obtained using the developed technique were in satisfactory agreement with those given by the rate diffusion turbidimetry.