A Participant in UK Biobank is a member of the British public who attended an Assessment Centre and consented there for UK Biobank to collect and manage appropriate relevant information about them.

The participants property of a Data-Field is the number of UK Biobank participants on whom that particular item of data is held. Except for baseline data-fields, this number will generally be less than the total number of participants in UK Biobank since, for various reasons, not everyone took part in every investigation or measurement.