A purified fraction of bovine lecithin (PBL), which has previously been shown to possess many wide ranging biological activities, has now demonstrated an ability to effectively inhibit viral infection as determined by the plaque reduction assay. Prior to infection of host tissue culture cells, several dosages of PBL were incubated with a fixed titer of virus for various times and temperatures. The experiments showed the inhibition to be dosage and time dependent, but not temperature dependent. During infection of host cells, the cells were exposed to minute amounts of PBL for a short period, and so there is a possibility that PBL may also be affecting the cells themselves, which is currently being investigated. It was noted that even as small an amount as 1 μg PBL/ml incubated with the virus produced significant inhibition.