A granule is a small grain. In describing cells, a granule may be any structure barely visible by light microscopy, but most often a secretory vesicle.

A group of leukocytes called granulocytes contain granules and play an important role in the immune system. The granules of certain cells, such as Natural Killer Cells, contain components which can lead to the lysis of neighboring cells.

See also

• Dense granule
• Chromaffin granule

Organelles