A boundary-value problem concerning the primary viscometric flow between rotating parallel disks is formulated and solved for microdisperse liquids displaying apparent slip at wall. Existing simplified analyses are identified with the narrow-gap asymptote to the exact solution. A simple method of converting primary torque and thrust data to the related viscometric material functions (fluidity, slip extrapolation length, normal-stress differences) is suggested. (c) 2004 Elsevier B.V. All rights reserved.