Smad proteins are the central feature of the TGF-ß intracellular signaling cascade. They function by carrying signals from the cell surface to the nucleus through the formation of a series of signaling complexes. Changes in Smad proteins and their complexes upon treatment with TGF-ß were studied in mink lung epithelial (Mv1Lu) cell cultures. A time course of incubation with TGF-ß was carried out to determine the peak of appearance of phosphorylated Smad2. Immobilized monoclonal antibody against Smad2 was then used to isolate the naturally occurring complexes. Three strategies were employed to identify changes in proteins partnering with Smad2: separation by 1D SDS-PAGE, followed by MALDI peptide mass fingerprinting, cICAT labeling of the protein mixtures analyzed by LC-MS/MS, and nano-LC followed by MALDI MS-TOF/TOF. Smad2 forms complexes with many other polypeptides both in the presence and absence of TGF-ß. Some of the classes of proteins identified include: transcription regulators; proteins of the cytoskeletal scaffold and other tethering proteins; motility proteins; proteins involved in transport between the cytoplasm and nucleus; and a group of membrane adaptor proteins. While some of these have been reported in the literature, most have not been previously reported. This work expands the repertoire of proteins known to participate in the TGF-ß signal transduction processes.