A study of tissue samples from 161 marine mammals that died between 2004 and 2009 in the Pacific Northwest reveals an association between severe illness and co-infection with two kinds of parasites normally found in land animals. One, Sarcocystis neurona, is a newcomer to the northwest coastal region of North America and is not known to infect people, while the other, Toxoplasma gondii, has been established there for some time and caused a large outbreak of disease in people in 1995.