Paralytic shellfish poisoning is caused by the ingestion of shellfish meat rendered toxic by exposure to a high level of toxic dinoflagellates during the phenomenon of "red tide". This paper reports the first outbreak of paralytic shellfish poisoning from green mussels in Singapore which resulted in two deaths. Analysis of the mussel meat by a standardised mouse bioassay confirmed the presence of the toxin. An attempt was also made to extend the bioassay to an analysis of the gastrointestinal contents. The clinical features of the condition are presented.