This dataset gives concentrations of chemical contaminants in the contents of eggs collected from colonies of the northern gannet, Morus bassanus, in the United Kingdom. The majority of eggs analysed are from colonies on Ailsa Craig (Firth of Clyde) and Bass Rock (Firth of Forth) and have been collected since 1971. The study examined 658 eggs collected between 1971 and 2009. Eggs analysed by the PBMS are collected by licensed collectors. Contaminants measured include organochlorine pesticides, total mercury, total PCBs and, for recent years, individual PCB congeners. The PBMS is a long-term, national monitoring scheme that quantifies the concentrations of contaminants in the livers and eggs of selected species of predatory and fish-eating birds in Britain. Levels of contaminants are monitored to determine variations between species and regions, changes over time and effects on individual birds and their populations. The Scheme is funded by CEH, Natural England, the Environment Agency (EA) and the Campaign for Responsible Rodenticide Use (CRRU). Full details about this dataset can be found at https://doi.org/10.5285/2ddf56e5-fbcd-48a3-b4a5-fe2a7d5c90a4