To develop a rapid and multisample analysis system for latex immunoassay with submicroliters of sample, an array of microreactors were fabricated using micromachining techniques including photolithography, anisotropic etching, and thin gold film deposition. The chamber volume for immunoreactions of a single well was 0.4 microL. An alternating-current (ac) field was used to enhance the rate of the latex agglutination reaction. By applying an ac field for 1 min, alpha-fetoprotein in several samples could be determined simultaneously. The detection limit in this system was approximately 10 pg/mL.