Abstract: A rotor and stator mixing system has mixing-chamber recesses in the outer periphery of the rotor and inner periphery of the stator which are generally similar, arrayed in peripheral and axial rows and are mutually axially offset. The guide radius R of the semicircular ends of each elongated recess is also the trough radius thereof and the trough depth is less than this guide radius. The length L of the mixing chambers is three to four times the guide radius, the web width between the recesses of each circumferential row is less than half the guide radius and the shear gap width W is so selected that the shear velocity which is realized is sufficient for effective mixing by a shear action.