Figure 1. Photograph of a hemagglutinin assay plate for NDV-LS. The HA titer was determined as described in the Methods section. Two-fold serial dilutions of NDV-LS stock were added to the wells in duplicate in a microtiter plate. The greatest dilution in which erythrocyte agglutination still occurred was either 1/2,560 or 1/5,120. This represents 102,400-204,800 HA units/mL.