Syk, one of the well known protein tyrosine kinases, is widely expressed and plays an important role in intracellular signal transduction in hematopoietic cells (1–3). Syk has been shown to interact with immunoreceptor tyrosine–based activation motifs (ITAMs) located in the cytoplasmic domains of immune receptors (4). It couples the activated immunoreceptors to downstream signaling events that mediate diverse cellular responses, including proliferation, differentiation and phagocytosis (4). There is also evidence of a role for Syk in nonimmune cells, and Syk may be a potential tumor suppressor in human breast carcinomas (5). Tyr323 is a negative regulatory phosphorylation site within the SH2-kinase linker region in Syk. Phosphorylation of Tyr323 provides a direct binding site to the TKB domain of Cbl (6,7). The Tyr352 residue in Syk is involved in the association of PLC-g1 (8). Tyr525/526 are located in the activation loop of Syk kinase domain, phosphorylation of Tyr525/526 of human Syk (equivalent to the Tyr519/520 of mouse Syk) is essential for Syk function (9). Phospho-Syk Sampler Kit provides an economical means to evalute the activation status of Syk, including the phosphorylation of Tyr323, Tyr352, and Tyr525/526. The control Syk Antibody is also included. The kit contains enough primary and secondary antibodies for two mini-blot experiments.