Viruses originating in human fecal pollution that are carried by shellfish can lead to serious health hazards.  Existing sanitation standards rely on the detection of bacteria, not viruses, present in feces.  Norwalk-type viruses (NLV) and hepatitis A virus (HAV) have been the most common viral shellfish-associated disease agents.  The goals of this research were to develop an invective assay for NLV and other caliciviruses and to develop an immunocapture reverse-transcriptase polymerase chain reaction (RT-PCR) assay for the detection of these viruses in shellfish.  Approaches explored for the invectivity assay included evaluation of primary and continuous cell lines, of different additives and physical conditions, and of different methods of virus inoculum preparation.   None of these approaches provided consistent evidence of virus replication.   However, an immunocapture RT-PCR assay for the detection of Norwalk virus was developed along with modifications of the RT-PCR assay to improve its performance characteristics.  The new assay allows the detection of Norwalk virus added to shellfish tissues.