This dataset contains plaque reduction neutralisation test (PRNT) results for common guillemot (Uria aalge) blood samples tested against twelve strains of a tick-borne virus, Great Island virus. 144 individual pre-breeding and breeding guillemots were captured between 1993 and 1995 on the Isle of May, Scotland and blood samples collected on filter paper. Plaque reduction neutralisation tests (PRNT) were then performed on these blood samples to detect virus strain-specific neutralising antibodies. Part of this dataset is presented in the peer-reviewed article Nunn et al. (2006) Parasitology 132: 233-40. This work was part of a NERC-funded PhD project looking at interactions between avian colonial social structure and tick-borne pathogen dynamics.