Analytical reaction cassette and method for performing sequential analytical assay procedures to determine the amount of an analyte in a liquid test mixture. The reaction cassette (10) can be in the form of a substantially square container having a substantially horizontal axis of rotation and incorporated with one or more analytical reagents such that they are contacted with a liquid test mixture in a desired ordered sequence to perform a particular assay procedure. Corners (22-24) provided by the substantially square configuration of the reaction cassette disrupt the flow of liquids disposed in the reaction cassette upon contact therewith to thereby agitate and mix such liquids. A liquid disposed in the reaction cassette is capable of being manipulated and mixed therein by rotating the reaction cassette about the horizontal axis at sufficiently low velocities wherein the transport of such liquid is noncentrifugal and due substantially only to gravitational force. The reaction cassette is particularly useful for performing immunoturbidimetric assays, e.g., for the determination of glycated hemoglobin.