The primary role of the kidneys is to filter waste products from the blood and regulate the body's fluid balance. They play a crucial role in maintaining homeostasis by adjusting the levels of electrolytes, such as sodium and potassium, and ensuring proper hydration. Additionally, the kidneys produce hormones like erythropoietin, which stimulates red blood cell production, and renin, which helps regulate blood pressure. Overall, kidney function is essential for metabolic processes and overall health.