Tandem mass spectrometry is a powerful technique for the identification of proteins contained in a biological sample. We present a grid-based application service for the analysis of tandem mass spectra, based on the open-source X!Tandem algorithm. The implemented parallelization strategy allows the distribution of analysis jobs to a grid of desktop PCs, utilizing their idle capacity. For this application service, a user-friendly project-oriented frontend was developed, implemented as a web-based workspace. After analysis, results are visualized and presented to the user along with a set of powerful and novel tools to allow further interpretation and evaluation of search results.