Techniques are described for the growth and characterization of some mammalian coronaviruses. Because of the fastidious nature of their growth requirements, most will replicate only in cells derived from the natural host or a closely related species. Fetal cat cells are used to grow FIPV, and porcine cells are used to grow TGEV and HEV. However, CCV will replicate in both feline and canine cells. Although all four of these viruses prefer to replicate in a cell in the stationary phase of growth, FIPV is able to replicate in an actively growing cell. Each virus causes a cytopathic effect in monolayer cell cultures under agar or media 18 to 72 h postinfection. Primary isolation of each virus from field specimens is difficult, although most can usually be isolated after 1 to 3 blind passages in the cell culture.