Concentrated, low-viscosity, low-volume liquid pharmaceutical formulations of proteins have been developed. Such formulations can be rapidly and conveniently administered by subcutaneous or intramuscular injection, rather than by lengthy intravenous infusion. These formulations include low-molecular-weight and/or high-molecular-weight proteins, such as mAbs, and viscosity-lowering agents that are typically bulky polar organic compounds, such as many of the GRAS (US Food and Drug Administration List of compounds generally regarded as safe) and inactive injectable ingredients and FDA approved therapeutics.