Oocytes released en masse from pig ovaries were isolated in large quantities by using sieving techniques. The isolated oocytes were gently homogenized, and the largely intact zona pellucida ghosts were purified by using sieving techniques. Sufficient amounts of zonae were recovered to permit, for the 1st time, adequate characterization of the zona pellucida in chemical, physical and macromolecular terms. The isolated zonae were > 93% pure as determined by chemical, enzymatic and microscopic criteria. The zonae were completely solubilized by a variety of conditions that do not break covalent bonds. The extent of solubilization was a function of pH, ionic strength, temperature and the presence of various solubilizing agents such as detergents and urea. Chemically, the zonae were composed predominantly of protein (71%) and carbohydrate (19%). After acid hydrolysis of the zonae, no unusual amounts or types of amino acids were detected. The monosaccharides present after hydrolysis were those typically found in animal glycoproteins (Fuc, Man, Gal, GalNAc and GlcNAc). Sialic acid in glycosidic linkage and sulfate and phosphate esters were present and were considered to be true constituents of the zona pellucida. Other substances detected, but considered contaminants rather than true constituents, included fatty acids (esterified and free) and uronic acids. The binding by several fluorescein-conjugated plant lectins to the in situ zona pellucida was determined by using light microscopy. The binding of the lectins to the zona pellucida was not uniform, indicating that the carbohydrate moieties of the zona pellucida were asymmetrically distributed. The zona pellucida was composed of at least 3 macromolecules indicated by immunodiffusion and sodium dodecyl sulfate gel electrophoresis experiments. Determination of the number of macromolecules composing the zona pellucida was compromised by the aggregation and/or microheterogeneity of its constituent macromolecules. The zona pellucida is evidently composed of several glycoprotein macromolecules; interaction of these macromolecules to form supramolecular complexes and the integral zona pellucida is dependent on noncovalent forces.