The influence of the incubation period and the amount of antigen on the haemagglutination inhibition titres to Newcastle disease virus.

An investigation was made into the significance of incubation period and amount of antigen used in the haemagglutination inhibition (HI) test for Newcastle disease virus in chicken serum. Also the results of a manually performed macrotest were compared with those of an automated microtest. Both incubation period and amount of antigen greatly influenced the HI titres. In incubating sera the titres increased up to 75 or 120 minutes when respectively 2 or 4 haemagglutinating units per volume were used. By contrast they became stable after 45 minutes' incubation with 8 units per volume. It was concluded that the latter combination gave optimum results. There were no significant differences between the results obtained with the macro and the micro technique.