Objective To compare blood mercury concentrations of infertile couples with those of fertile couples in Hong Kong, and to examine the relationship between blood mercury concentrations and seafood consumption.

Design Case–control study.

Setting In vitro fertilisation (IVF) Unit and Antenatal Unit of a university teaching hospital.

Sample One hundred fifty-seven infertile couples attending IVF treatment and 26 fertile couples attending antenatal care without known occupational exposure to mercury.

Methods Mercury concentrations in whole blood were measured by cold vapour atomic absorption spectrophotometry. A dietitian recorded the quantity of seafood consumption among infertile couples via a food-frequency questionnaire. Blood mercury concentrations and quantity of seafood consumption were compared between infertile and fertile couples.

Main outcome measures Whole blood mercury concentrations, quantity of seafood consumption.

Results Infertile couples had higher blood mercury concentrations than fertile couples. ‘Infertile males with abnormal semen’ and ‘infertile females with unexplained infertility’ also had higher blood mercury concentrations than their fertile counterparts. Blood mercury concentrations were positively correlated with quantity of seafood consumption. Infertile subjects with elevated blood mercury concentrations consumed a larger amount of seafood.

Conclusion Higher blood mercury concentration is associated with male and female infertility. Higher seafood consumption is associated with elevated blood mercury concentrations in our infertile population.