The objective was to develop extraction and assay methods for recovering known caliciviruses from various tissues of shellfish given a measured quantity of virus, and to test for calicivirus replication in shellfish exposed to various known caliciviruses.   Molluscan shellfish are known to be contaminated with several potential human pathogens including the caliciviruses, which have been implicated in severe outbreaks of viral gastroenteritis.  Lack of specific, reliable tests for caliciviruses and other pathogens has resulted in shellfish waters being closed to harvesting because the status of contamination could not be determined.  Furthermore, decontamination methods of relaying and depuration have proven to be inadequate for insuring the safety of raw shellfish contaminated with caliciviruses.  Under this project, caliciviruses were isolated from naturally and experimentally exposed shellfish stocks using mammalian cell culture systems.  Retention (and possible replication) of these viruses in shellfish was demonstrated for 60 days or more under depuration using continuous flow sterile sea water.  The project also demonstrated that caliciviruses occur naturally within ocean sources including shellfish, and identified calicivirus contamination in both open and closed shellfish beds on all coasts ( Atlantic, Gulf, and Pacific), although the source of these viruses (marine and terrestrial) remains unknown.