Understanding networks of interacting proteins is a major goal in cell biology. The survival of motor neurons protein (SMN) interacts, directly or indirectly, with a large number of other proteins and reduced levels of SMN cause the inherited disorder spinal muscular atrophy (SMA). Some SMN interactions are stable and stoichiometric, such as those with gemins, while others are expected to be transient and substoichiometric, such as the functional interaction of SMN with coilin in Cajal bodies. This study set out to determine whether novel components of the extensive SMN interactome can be identified by a proteomic approach. SMN complexes were immuno-precipitated from HeLa nuclear extracts, using anti-SMN monoclonal antibody attached to magnetic beads, digested with trypsin, separated by capillary-liquid chromatography and analyzed by MALDI TOF/TOF mass spectrometry. One-hundred and one proteins were detected with a p value of