China 
Africa 
- Afimoxifene
- Aflatoxin B1
- Aflibercept
- African Palliative Care Association
- African histoplasmosis
- African meningitis belt
- African swine fever
- African swine fever virus
- African tick bite fever
- African trypanosomiasis
- African-American hair
- Aftercare
- Afterdepolarization
- Afterhyperpolarization
- Afterimages
- Afterload
- Aftershave
- Afzelechin
- AgNO3
- Agalactia
- Agalsidase alfa
- Agalsidase beta
- Agammaglobulinemia
- Aganglionosis
- Agar
- Agar dilution
- Agar plates
- Agarase
- Agaricus blazei
- Agarose
- Agarose gel electrophoresis
- Agarwood
- Agatston score
- Agave
- Age distribution
- Age of onset
- Age structure
- Age-1
- Age-related hearing loss
- Age-related macular degeneration
- Age-related memory loss
- Aged care
- Ageing
- Ageing population
- Ageless
- Agenesis
- Agenesis of the corpus callosum
- Agent Orange
- Ageusia
- Agger nasi
- Agglutination
- Agglutination tests
- Agglutinin
- Aggrecan
- Aggrecanase
- Aggregate
- Aggregatibacter
- Aggregatibacter actinomycetemcomitans
- Aggregation-induced emission
- Aggresomes
- Aggression
- Aggression Replacement Training
- Aggressive NK cell leukemia
- Aggressive NK-cell leukemia
- Aggressive angiomyxoma
- Aggressive fibromatosis
- Aggressive lymphoma
- Aggressive periodontitis
- Aging
- Aging in place
- Aging-associated diseases
- Agitated depression
- Agitation
- Aglycones
- Agmatinase
- Agmatine
- Agnosia
- Agnuside
- Agomelatine
- Agonal respiration
- Agonist muscle
- Agonist-antagonist
- Agonists
- Agoraphobia
- Agouti
- Agouti gene
- Agouti related protein
- Agouti-related peptide
- Agouti-related protein
- Agrammatism
- Agranulocytes
- Agranulocytosis
- Agraphesthesia
- Agraphia
- Agricultural runoff
- Agrimonia
- Agrimonia pilosa
- Agrin
- Agrobacterium
- Agrobacterium rhizogenes
- Agrobacterium tumefaciens
- Agroinfiltration
- Agronomic trait
- Agyria
- Aicardi Goutieres Syndrome
- Aicardi syndrome
- Air abrasion
- Air bronchogram
- Air compressors
- Air crescent sign
- Air density
- Air displacement plethysmography
- Air embolism
- Air pollutant concentrations
- Air pollutants
- Air pollution
- Air purifiers
- Air quality
- Air sac
- Air toxics
- Air transport
- Air trapping
- Air-abrasion
- Airborne transmission
- Airflow
- Airlocks
- Airsacculitis
- Airspeed
- Airtraq
- Airway
- Airway clearance technique
- Airway clearance therapy
- Airway constriction
- Airway management
- Airway obstruction
- Airway resistance
- Ajmalicine
- Ajmaline
- Ajulemic acid
- Ajwain
- Akathisia
- Akebia
- Akebia quinata
- Akinesia
- Akinete
- Akinetic mutism
- Akinetopsia
- Akkermansia
- Akkermansia muciniphila
- Akr1c1