The invention describes a method for the identification of compounds which
bind to a target component of a bio-chemical system or modulate the
activity of the target, comprising the steps of: a) compartmentalising
the compounds into micro-capsules together with the target, such that
only a subset of the repertoire is represented in multiple copies in any
one microcapsule; and b) identifying the compound which binds to or
modulates the activity of the target; wherein at least one step is
performed under microfluidic control. The invention enables the screening
of large repertoires of molecules which can serve as leads for drug
development.