The French authorities have launched an investigation following the death of two people who had eaten oysters in the town of Arcachon, south-west France.
Oyster farmers are angry at the ban
The two - aged 66 and 77 - died in separate incidents during the week.
So far, no link has been established between the deaths and eating the shellfish, authorities say.
Concern was raised because of the ban on the sale and consumption of Arcachon bay oysters imposed in August after tests revealed a high level of toxins.
It is the third oyster ban in the last 18 months in the region of Arcachon, which is famous for its oysters - although it is not clear where the toxins come from.
This has angered local farmers, who say the ban is affecting their livelihood.
In response, farmers staged a mock funeral procession "in memory of the oyster growers" on Wednesday before learning of the two people who had died after eating oysters.
"We are completely aghast. To my knowledge, in the world no-one has ever died of oysters," Marc Druarat, head of the Arcachon oyster association said.
The agriculture ministry said the ban would be maintained following the two deaths.
Arcachon bay is oyster country
Doctors say nothing could be said for certain. Further forensic test are being carried out.
"We should not jump to conclusions", a health ministry spokesperson said in Paris.
Farmers claim the test on mice which measures the level of toxins in oysters is outdated and point out that the same toxins have not been found in the waters where the shellfish is farmed.
Authorities say the procedure will remain in place until new chemical tests have been developed - probably by the end of 2007.
Oyster cultivation is one of the main industries in Arcachon, employing about 1,000 people in small farms and producing 10,000 tonnes of oysters every year.