The flow of power law fluids for isothermal, laminar flow in concentric annuli was investigated experimentally and numerically. Similar to the results of Russel & Christiansen (1974, Indust. Engng Chem. Process Des. Develop. 13, 391-398) it was observed that plots of the natural logarithm of a reduced shear stress at the outer wall of the annulus vs the natural logarithm of a reduced pseudo-shear rate were identical to those for tube flow. However; in contrast to the findings of Russel & Christiansen (1974), the y intercepts and the slopes of these plots were found to be equal to In K＇ and n, respectively. Frederickson & Bird＇s (1958, Indust. Engng Chem. 50, 347-352) solution was found to be in perfect aggreement with the numerical solution in every case. The Hanks & Larsen (1979, Indust. Engng Chem. Fundamentals, 18, 33-35) equation also agreed very well with the numerical solution. The Russel & Christiansen (1974, Indust. Engng Chem. Process Des. Develop., 13, 391-398) method gave an absolute mean error of 3.6% against the numerical results for pressure drop.