The composition of individual human zonae pellucidae and modifications to this extracellular coat both before and after fertilization were analysed using a rapid, sensitive, non-radioactive biotinylation- or lectin-based detection system; these assays use commercially available reagents and can be performed on fragments of individual zonae pellucidae. The zona pellucida from unfertilized eggs is composed of three glycoprotein species designated as huZP1, huZP2 and huZP3. Under non-reducing conditions, the molecular weights of these proteins are approximately 150 kDa, approximately 100 kDa, and approximately 55-65 kDa respectively. Following fertilization, huZP1 was not detected under either non-reducing or reducing conditions. In contrast, after fertilization huZP2 was detected under non-reducing conditions, but not under reducing conditions. The ability to detect pre- and post-fertilization changes in a single human zona pellucida is discussed in relation to its value in assessing deficiencies in clinical and laboratory protocols used for in-vitro fertilization.