Wild grey squirrels in North Wales were examined for their serological response to a range of laboratory mouse pathogens. Nineteen squirrels were tested against 14 organisms and a high seroprevalence was found to several, including murine cytomegalovirus, mouse adenovirus, reovirus 3, rotavirus and Sendai virus. Four of the squirrels were seropositive for lymphocytic choriomeningitis virus, a zoonotic pathogen. None of the infections has previously been reported in squirrels.