The enzymatic digestion of cellulosic biomasses, such as corn stover and switchgrass, to create biofuels, such as ethanol, is economically competitive only when working at high solids fractions. Therefore, the production of cellulosic ethanol involves working with high-solids slurries, which are notoriously difficult to transport due to their high viscosity, requiring large, powerful pumps. As a result, it is particularly important to understand the rheological properties of these slurries. In this work, we examine the rheology of high-solids biomass slurries as a function of the critical variables for biorefining. Acid hydrolyzed corn stover slurries are investigated and found to exhibit properties characteristic of soft solids, including an apparent yield stress and shear thinning behavior. Rheological properties were examined using vane-in-cup and parallel plate geometries. Special care is taken to account for or avoid wall slip in the rheological measurements. Shear thinning behavior and an apparent yield stress on the order of 1000 Pa were observed, and the Herschel-Buckley model was used to characterize the data. Rheological properties of the slurries were also measured during enzymatic hydrolysis. Interestingly, preliminary measurements suggest that viscosities do not decrease monotonically with the degree of cellulose conversion (digestion time). An attempt was made to correlate the slurries' rheological properties with the enzymatic hydrolysis of cellulose and the molecular interactions between the slurry particles. Thus, “enzo-rheology” combines enzyme kinetics, rheology and microscopy to capture the breakdown of fibrous cellulosic biomasses and the processability of the slurries.