Micromixing in a static mixer and an empty tube was characterized by the product distribution of fast consecutive competing reactions. As a test reaction, the pptn. of BaSO4 complexed by EDTA in alk. medium under the effect of an acid was used. The acid was injected at a point of the reactor into an excess of basic complex. The pptd. BaSO4 is a measure of the degree of segregation which can be characterized by an index Xs, representing the amt. of macrofluid in the partially segregated fluid. Expts. were carried out in a tubular reactor and in a static mixer in the laminar flow regime (0.4 < Reynolds no. < 300) by varying the fluid viscosity (10-3 < m < 26 * 10-3 kg/ms) and the flow rate. Furthermore, the characteristic reaction time tr was varied from .apprx.1 to 75 s. Depending on the exptl. conditions, the Xs was 0.1-0.3 for the mixer and from 0.2-0.75 for the empty tube. The micromixing time, tm, was deduced from Xs and tr. The mixing tm was .apprx.10 times larger in an empty tube than in the static mixer. [on SciFinder (R)]