A method for determining the effect of a plurality of culture conditions on a cell, comprising the steps of: a) providing a first set of groups of cell units each comprising one or more cells, and exposing said groups to desired culture conditions; (b) pooling two or more of said groups to form at least one second pool; (c) subdividing the second pool to create a further set of groups of cell units; (d) exposing said further groups to desired culture conditions; (e) optionally, repeating steps (b)-(d) iteratively as required; and (f) optionally assessing the effect on a given cell unit of the culture conditions to which it has been exposed.