A method of selecting a monoclonal cell colony that secretes a product of interest, comprising: providing a plurality of cell culture spaces, each cell culture space having a respective assessment surface, wherein said cell culture spaces are respective wells of a multi-well culture plate, or respective separate culture vessels; providing each said assessment surface with a first binding agent that is immobilised on the assessment surface; plating a suspension of cells in the plurality of cell culture spaces; incubating the cells in a growth medium in the cell culture spaces to cause replication of the cells, wherein at least some of the cells secrete a product of interest; providing a second binding agent in the cell culture spaces, the second binding agent not being immobilised; wherein each of the first and second binding agents binds to the product of interest so that secretion of the product of interest by cells in any one of the cell culture spaces leads to a complex comprising the first binding agent, the product of interest and the second binding agent forming at the corresponding assessment surface of the said one cell culture space; assessing each of at least some of the cell culture spaces for presence of the second binding agent at the assessment surface of the cell culture space; characterised in that said plating of said suspension of cells in said plurality of cell culture spaces is such that at least some of the cell culture spaces are plated with one cell and one cell only; by determining for each of at least some of the cell culture spaces whether the cell culture space contains a single cell colony that is derived from a single cell; wherein for each of said at least some cell culture spaces for which said determination is performed said determination comprises determining whether the cell culture space was plated with one cell and one cell only by microscopic visualisation of cells in the cell culture space at a plurality of time points during said incubation; and by selecting a cell culture space, the selected cell culture space having being identified by said determination and said assessment as containing a single monoclonal cell colony which secretes the product of interest, and wherein said selected cell culture space was plated with one cell and one cell only. providing a plurality of cell culture spaces, each cell culture space having a respective assessment surface, wherein said cell culture spaces are respective wells of a multi-well culture plate, or respective separate culture vessels; providing each said assessment surface with a first binding agent that is immobilised on the assessment surface; plating a suspension of cells in the plurality of cell culture spaces; incubating the cells in a growth medium in the cell culture spaces to cause replication of the cells, wherein at least some of the cells secrete a product of interest; providing a second binding agent in the cell culture spaces, the second binding agent not being immobilised; wherein each of the first and second binding agents binds to the product of interest so that secretion of the product of interest by cells in any one of the cell culture spaces leads to a complex comprising the first binding agent, the product of interest and the second binding agent forming at the corresponding assessment surface of the said one cell culture space; assessing each of at least some of the cell culture spaces for presence of the second binding agent at the assessment surface of the cell culture space; characterised in that said plating of said suspension of cells in said plurality of cell culture spaces is such that at least some of the cell culture spaces are plated with one cell and one cell only; by determining for each of at least some of the cell culture spaces whether the cell culture space contains a single cell colony that is derived from a single cell; wherein for each of said at least some cell culture spaces for which said determination is performed said determination comprises determining whether the cell culture space was plated with one cell and one cell only by microscopic visualisation of cells in the cell culture space at a plurality of time points during said incubation; and by selecting a cell culture space, the selected cell culture space having being identified by said determination and said assessment as containing a single monoclonal cell colony which secretes the product of interest, and wherein said selected cell culture space was plated with one cell and one cell only.