A new method was used for determining the active nuclear polyhedrosis virus content of untreated marketable cabbages. The activity of the virus was determined by inter-polating the dose-mortality data obtained from bioassays of homogenized wrapper leaves, heads, and whole cabbages. An average of 4.61 × 103active polyhedra/g of cabbage was obtained from untreated edible cabbage heads assayed in 1972.