The sialylation pattern of serum ฮฑ1-acid glycoprotein (AGP) in non-symptomatic cats infected by feline coronavirus (FCoV) and its possible relationship with the amount of FCo. Vs shed in faeces were investigated. Blood from three specific pathogen-free cats (group A) and from 10 non-symptomatic FCoV-positive cats from catteries with low (group B, three cats) or high (group C, seven cats) levels of faecal shedding were collected monthly. AGP was purified from serum and Western blotting followed by lectin-staining of ฮฑ(2,3)-linked and ฮฑ(2,6)-linked sialic acid. Faecal shedding was quantified in group C by quantitative polymerase chain reaction. Variations of AGP sialylation were recorded only in cats from group C, on which viral shedding peaked before the occurrence of feline infectious peritonitis (FIP) in the cattery, and decreased 1 month later, when serum AGP had an increase of ฮฑ(2,3)-linked sialic acid. These results suggest that hypersialylation of AGP may be involved in host-virus interactions. ยฉ 2008 ESFM and AAFP.