Smad transcription factors lie at the center of the transforming growth factor-beta (TGFβ) pathway, which is one of the most important cytokine signaling pathways. Members of the transforming growth factor-beta (TGFβ) superfamily bind to serine/threonine kinase receptors and specifically activate intracellular Smad proteins. Smads 2 and 3 are activated by activin/nodal and TGFβ, whereas Smads 1, 5 and 8 are activated by TGFβ-like BMP (Bone morphogenetic proteins). Smads family can be subsequently classified based on their activation by TGFβ or BMP cytokine family. These activated Smads form the complexes with co-Smads, translocate from cytoplasm into nucleus and bind to the distinctive consensus binding sequences on the target promoter region to regulate the transcription of genes. Signosis has developed the Smad2/3 ELISA kit for the analysis of the TGFβ/Smad pathway, Smad1/5/8 ELISA kit for the analysis of the BMP/Smad pathway, and a combined kit (48 wells for Smad2/3 and 48 wells for Smad1/5/8) to facilitate studying activation of different Smad-related pathways.