The time required for the laboratory diagnosis of Newcastle disease has been the object of criticism from the practical point of view. Of the three principal diagnostic methods employed, virus isolation and neutralization tests are carried out in embryonating chicken eggs; the hemagglutination-inhibition test is done in test tubes. The present communication describes a plate hemagglutination-inhibition test which has been used in this laboratory in comparison with the aforementioned serologic tests for the past year. Literature. The phenomenon that influenza virus agglutinates chicken red cells and that specific antibodies inhibit such agglutination, was first described by Hirst (1941). Burnet (1942) demonstrated that Newcastle disease virus shows similar properties. A quantitative measurement of the hemagglutination-inhibiting antibodies for Newcastle disease in chicken serums was described by Florman (1947). For the routine test tube hemagglutination-inhibition (HI) test the latter method was followed except that serums were not inactivated and 16 (instead of 32) . . .