Abstract: Results are presented for a math. simulation of the process of circulation of a substance in a reaction tube of a system for flow-injection anal. in the presence of a chemical reaction under conditions of an excess of 1 of the reagents. By using the method of moments, an anal. expression was obtained (for the 1st time) for the amt. of the substance, the coordinates of the max., and the dispersion of the peak not only for the sample introduced into the channel but also for the products of the chemical reaction. The problem is discussed concerning the effect of the channel parameters, as well as those of the sample and products, on the dispersion of the substance and on the use of the given theory in the task of optimizing flow-injection anal. (SFS)