Phenomenon occasionally observed in agglutination or other tests involving progressive dilutions of serum. Some or all of the lower (stronger) dilutions show a negative result, whereas the higher dilutions are positive. The illogically negative series of dilutions is the prozone.
Portion of the low dilution range of a homologous serum that fails to agglutinate bacteria that are agglutinated by the same serum in a higher dilution.