The use of proteome-expression databases may facilitate cancer research. Proteome-expression data derived from a sufficient number of clinical cases may help establish the molecular background of malignant tumors. Recently, we published a proteome expression database, the Genome Medicine Database of Japan (GeMDBJ) Proteomics. The GeMDBJ Proteomics includes the proteome data of surgically resected tissues and tissue-cultured cells of various malignancies, as well as the corresponding biological and clinicopathological data. The proteome data in GeMDBJ Proteomics include expression data produced using 2D PAGE with the immobilized pH gradient gel and DIGE technology, and the protein identification data by liquid chromatography tandem mass spectrometry. GeMDBJ Proteomics can be freely accessed online without registration.