Early in 1981, cases of hepatitis possibly associated with the consumption of cockles were reported mainly from south-east England. A case-control study was undertaken in 19 local authority districts. Between Nov. 1, 1980, and April 30, 1981, 424 cases of infective jaundice were formally notified and case-finding yielded 26 additional cases. 42.6% of those with hepatitis and 17.5% of the controls reported consumption of cockles. There was a statistically significant association between infective jaundice and the consumption of cockles but not other sea foods. The cockles had probably been insufficiently processed and stricter controls on treatment of such shellfish are needed.