Grey seal (Halichoerus grypus) pups can receive substantial doses of organochlorine contaminants during lactation. This exposure may cause immunosuppression. We studied the effect of exposure to individual chlorobiphenyl (CB) congeners on grey seal pups at the Isle of May in the Firth of Forth, Scotland, by monitoring the prevalence of non-specific infection in pups, and by measuring perturbations in various haematological and biochemical blood parameters. There was no relationship between the prevalence of infection in pups, as a sign of immunosuppression, and the cumulative lactational dose of CB congeners. There was also no relationship between age at diagnosis of infection and CB dose, thus pups receiving relatively higher doses of contaminants early in life were no more likely to succumb to infection than those receiving lower doses. There was also no relationship between age-related changes in haematological and biochemical blood parameters and exposure to CB contaminants. Although pups which became infected with non-specific pathogens had received higher cumulative doses of CB on a toxicity equivalence basis than those which did not, this effect disappeared when results were corrected for the effect of pup age.