An attempt to collect, format, analyse and disseminate surveyed marine biological data deriving from the Eastern Mediterranean and Black Sea region is currently under development at the Hellenic Center for Marine Research (HCMR, Greece). The effort has been supported by the MedOBIS project (Mediterranean Ocean Biodiversity Information System) and has been carried out in cooperation with the Aristotelian University of Thessaloniki (Greece), the National Institute of Oceanography (Israel) and the Institute of Biology of the Southern Seas (Ukraine). The aim is to develop a taxon-based biogeography database and online data server with a link to survey and provide satellite environmental data. In its completion, the MedOBIS online marine biological data system (http://www.medobis.org/) will be a single source of biological and environmental data (raw and analysed) as well as an online GIS tool for access of historical and current data by marine researchers. It will function as the Eastern Mediterranean and Black Sea node of EurOBIS (the European node of the International OBIS initiative, part of the Census of Marine Life). The spatial component of data has led to the integration of datasets by means of the Geographic Information System (GIS) technology. The latter is widely used as the natural framework for spatial data handling. GIS serves as the basic technological infrastructure for several online marine biodiversity databases available on the Internet today. Developments like OBIS (Ocean Biodiversity Information System, http://www.iobis.org/), OBIS-SEAMAP (Spatial Ecological Analysis of Megavertebrate Populations, http://seamap.env.duke.edu) and FIGIS (FAO Fisheries Global Information System, http://www.fao.org/fi/figis) facilitate the study of anthropogenic impacts on threatened species, enhance our ability to test biogeographic and biodiversity models, support modeling efforts to predict distribution changes in response to environmental change and develop a strong potential for the public outreach component. In addition, such online database systems provide a broader view of marine biodiversity problems and allow the development of management practices that are based on synthetic analysis of interdisciplinary data. Towards this end, a new online marine biological information system is developed. MedOBIS (Mediterranean Ocean Biodiversity Information System) intends to assemble, formulate and disseminate marine biological data for the Eastern Mediterranean and Black Sea regions focusing on the assurance and longevity of historical surveyed data, the assembly of current and new information and the dissemination of raw and integrated biological and environmental data and future products through the Internet. To provide a taxon-based search capability to the MedOBIS development, the sampling data as well as the relevant spatial data are stored in the database, so taxonomic data can be linked with the geographical data by queries. To reference each species to its location on the map, the database queries are stored and added to the applet as individual layers. A search function written in JavaScript searches the attribute data of that layer, displays the results in a separate window and marks the matching stations on the map. Finally, selecting several stations by drawing a zooming rectangle on the map provides a list with predefined themes from which the user may select more information. As more data will be assembled in time-series databases, an additional future work will include the development of MedOBIS data analysis phase, which is planned to include GIS modeling/mapping of species-environment interactions.