Ten young partridges (Rhynchotus rufescens) were vaccinated with the lentogenic strain of Newcastle disease virus. Another eight unvaccinated birds were kept in close contact with the treated flock. Antibodies levels were measured over the course of 3 mo in all birds using the hemagglutination inhibition (HI) test and the liquid-phase blocking enzyme-linked immunosorbent assay (LPB-ELISA). The LPB-ELISA was standardized, and the results were compared with those obtained with the HI test. Antibodies increased after 23 days postvaccination in 16 birds with no side effects as determined by both the HI test and the LPB-ELISA.