- Range of motion
- Ranibizumab
- Ranimustine
- Ranitidine
- Rank
- Rank correlation
- Rank sum test
- Rankin Scale
- Ranking
- Ranolazine
- Ranson criteria
- Ranula
- Ranunculin
- Raoultella
- Rap1
- Rapamycin
- Rape
- Rape Trauma Syndrome
- Rapeseed
- Rapeseed oil
- Raphe
- Raphe nuclei
- Raphe nucleus
- Rapid amplification of cDNA ends
- Rapid diagnostic test
- Rapid eye movement sleep behavior disorder
- Rapid influenza diagnostic test
- Rapid response team
- Rapid sequence induction
- Rapid sequence intubation
- Rapid shallow breathing index
- Rapid strep test
- Rapid urease test
- Rapidly progressive glomerulonephritis
- Rare disease assumption
- Rare diseases
- Rare variants
- Ras protein
- Ras superfamily
- Ras-related protein
- Ras2
- Rasagiline
- Rasayana
- Rasburicase
- Rasch model
- Rash
- Rasmussen's encephalitis
- Raspberries
- Raspberry ketone
- Rastelli procedure
- Rat Park
- Rat-bite fever
- Rate of reinforcement
- Rate pressure product
- Rate ratio
- Rate-determining step
- Rate-limiting step
- Rate-of-living theory
- Rathke's cleft cyst
- Rathke's pouch
- Rating
- Rating of Perceived Exertion
- Rating scale
- Rating scales for depression
- Rationalization
- Rauvolfia serpentina
- Rauwolfia
- Rauwolscine
- Raven's Progressive Matrices
- Ravuconazole
- Ravulizumab
- Raw milk
- Raw sugar
- Raxibacumab
- Ray tracing
- Rayleigh scattering
- Raynaud phenomenon
- Raynaud's phenomenon
- Rayon
- Rays
- Razor
- ReNu
- Reabsorption
- Reaction coordinate
- Reaction formation
- Reaction kinetics
- Reaction mechanism
- Reaction rate constant
- Reaction time
- Reaction velocity
- Reaction yield
- Reactive airway disease
- Reactive arthritis
- Reactive attachment disorder
- Reactive center
- Reactive dyes
- Reactive gastropathy
- Reactive hypoglycemia
- Reactive intermediates
- Reactive lymphocytes
- Reactive nitrogen
- Reactive nitrogen species
- Reactive oxygen species
- Reactive sulfur species
- Reactogenicity
- Read
- Read code
- Reading
- Reading disability
- Reading epilepsy
- Reading frame
- Reading machine
- Reagent
- Reagent testing
- Real image
- Real time polymerase chain reaction
- Real world data
- Real world evidence
- Real-time quaking-induced conversion
- Realistic Conflict Theory
- Reality principle
- Reality therapy
- Reanimation
- Reassortment
- Rebamipide
- Reboxetine
- RecQ helicase
- Recall bias
- Recall memory
- Recall test
- Recency effect
- Receptive aphasia
- Receptive fields
- Receptivity
- Receptor
- Receptor agonist
- Receptor agonists
- Receptor antagonist
- Receptor down regulation
- Receptor editing
- Receptor modulators
- Receptor potentials
- Receptor protein
- Receptor site
- Receptor tyrosine kinase
- Receptor tyrosine kinase-like orphan receptor
- Receptor-mediated endocytosis
- Recessive dystrophic epidermolysis bullosa
- Recessive gene
- Recessive genes