- Antiseptics
- Antiserum and Antitoxin
- Antiviral Drugs
- Appert, Nicolas François (1750-1841)
- Archaea
- Arenavirus
- Armillaria ostoyae
- Asexual Generation and Reproduction
- Asilomar Conference
- Atomic Force Microscope
- Attractants and Repellents
- Autoimmunity and Autoimmune Disorders
- Autologous Banking
- Autotrophic Bacteria
- Avery, Oswald Theodore (1877-1955)
- Azotobacter
