Although a variety of signaling systems and signaling proteins have been described, cell specific expression of these structures has not yet been systematically studied. Human amnion, bronchial epithelial, fibroblast, glial, kidney, lymphocyte and mesothelial cells were subjected to two-dimensional-gel electrophoresis followed by analysis of protein spots by MALDI-TOF and subsequent identification by specific software. A series of well-documented signaling proteins showed cell specific expressional patterns. Five hypothetical proteins--hypothetical 37.5 kDa protein, similar to calsyntenin 1, hypothetical armadillo repeat/plakoglobulin ARM-repeat profile containing protein, 11 days embryo cDNA clone 2700084k13, hypothetical protein flj22171--so far predicted from their nucleic acid sequence only, were identified, complementing already reported signaling cascades. An analytical tool for the concomitant determination of a large series of signaling structures by an antibody independent protein-chemical method is provided.