Conditions have been defined under which the sperm binding capacity of the mouse zona pellucida can be measured. As a measure of the concentration of anti-zona antibodies the inhibition of sperm binding appears to be both repeatable and sensitive. Using this technique anti-zona antibody titres were monitored in 6 rats actively immunized with extracts of mouse ovarian tissue. These animals exhibited a rapid rise in anti-zona antibody titre following the induction of immunity, and an associated

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... gnificant (P < 0\m=.\05) decline in their fertility, both in relation to the proportions of animals exhibiting fertile matings and of matings resulting in conception. Three of the animals exhibited permanent sterility despite repeated exposure to fertile males. sperm-egg association in vitro it is necessary to establish conditions under which the sperm 0022-4251/81/060295-15S02.00/0