Which cells in human body have no nucleus?

Mature red blood cells (erythrocytes) in humans lack a nucleus. During their development in the bone marrow, the nucleus is extruded so that the cell can be packed with maximum hemoglobin to efficiently transport oxygen. The biconcave shape and the absence of nucleus and other organelles increase the surface area and flexibility for gas exchange and capillary passage. Muscle cells, phagocytic cells (like macrophages) and ciliated cells all retain nuclei.