Detection of viruses by inoculation of cell cultures may be based on plaque formation or production of cytopathic effects (CPE); other things being approximately equal, the two methods are equally sensitive (Kostenbader and Cliver 1973) . Limitations are the susceptibility of the inoculated cells to the virus that happens to be present, and the volume of inoculum that can be tested in single culture. Where more than one cell culture type was needed to cover the spectrum of viruses of concern, we tried mixing two types of cells in a single culture but later learned that the inoculum could be harvested from a cell culture of one type, after an appropriate adsorption period, and transferred to a culture of another type with little loss of infectivity, and that much larger volumes of inoculum than usual could be tested per cell culture flask, under the right conditions, by the CPE method Cliver 1977, 1986) .