A microflow apparatus has been built with a time resolution of 1 ms for mixing volumes of at least 80 &mgr;l per syringe. A time resolution of 3 ms is attained for mixing volumes of 10 &mgr;l per syringe. Equal volumes are mixed and concentration changes are observed photometrically using fiber optics for coupling light into and out of the observation tube having 1 mm diameter and 10 mm light path length. The reaction of ferrocytochromecwith ferrihexacyanide was used to calibrate the apparatus at 550 nm (10 nm half‐width). ©1995 American Institute of Physics.