Grass seeds are complex organs composed by multiple tissues and cell types that develop coordinately to produce a viable embryo. The identification of genes involved in seed development is of great interest, but systematic spatial analyses of gene expression on maize seeds at the cell level have not yet been performed. MASISH is an online database holding information for gene expression spatial patterns in maize seeds based on in situ hybridization experiments. The web-based query interface allows the execution of gene queries and provides hybridization images, published references and information of the analyzed genes. © The Author 2010. Published by Oxford University Press.