The primary role of the kidneys in the human body is to filter blood to remove waste products and excess substances, regulating essential body functions, such as fluid balance, electrolyte levels, and blood pressure. They produce urine, which transports metabolites and toxins out of the body. The kidneys also contribute to maintaining pH balance and are involved in the production of hormones like erythropoietin, which regulates red blood cell production. Thus, they play a vital role in homeostasis.