The present invention provides a method of identifying a gene product. The method comprises providing a multiplicity of cells comprising a first gene product. Preferably, the first gene product is produced in the multiplicity of cells by expressing a first exogenous nucleic acid sequence encoding the first gene product. A library of second nucleic acid sequences encoding second gene products is then introduced into the multiplicity of cells. The second nucleic acid sequences are expressed in the multiplicity of cells to produce the second gene products such that the first gene product and at least one of the second gene products contact. The method further comprises causing a complex to form between the first gene product, an affinity molecule that binds the first gene product, and at least one of the second gene products, and subsequently retrieving the complex. At least one second gene product of the complex then is identified.