A comprehensive rheological characterization of lithium lubricating greases modified with NCO-terminated polymers has been performed in this work, with special emphasis on the effect of temperature. With this aim, NCO-terminated polymers were prepared from several di- and tri-functional polyols and polymeric MDI. Afterwards, the reaction between terminal isocyanate groups and 12-hydroxystearate lithium soap, used as thickener for lubricating grease formulations, was promoted. Transient and steady-state viscous flow, rheodestruction and stress relaxation tests were performed on the different samples studied. In this sense, the influence that temperature, free NCO content, molecular weight, and functionality of the reactive polymers exert on the rheological response of lubricating greases was analyzed. The most important rheological modification was achieved by using the lowest molecular weight polymer. In general, NCO-terminated polymers significantly dampen the influence of temperature on the rheological functions of the additive-free lubricating grease. In some cases, the viscosity and/or viscoelastic functions even increase with temperature, especially in formulations with residual free NCO groups. Several experimental flow problems, such as fracture and sample expelling from the measuring tool, are generally found, more frequently in formulations with high NCO content. (C) 2010 Wiley Periodicals, Inc., J Appl Polym Sci 118: 693-704, 2010