prozone

[prōzōn′]
n.
  1. The phenomenon in which mixtures of specific antigen and antibody do not agglutinate or precipitate visibly because of an excess of either antibody or antigen.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.