Ovomucin participates in the ovomucin-gel-forming properties because of its shape and its ability to interact in a specific spatial organization. Purified from chicken egg-white by exclusion chromatography with Sephacryl S-300 and Sepharose CL-2B and analysed by light-scattering, it exhibited an Mr of about 40 x 10(6). This large Mr can be explained by the aggregation of polymers that can be degraded into 3 x 10(6)-Mr fragments by reduction with dithiothreitol. The values for hydrodynamic parameters such as Mr, radius of gyration, hydrodynamic radius, mass per unit length and combinations of them suggested that ovomucin is a linear and highly flexible molecule conferring upon it a random-coil-like structure in 0.2 M-NaCl solution. Analysis of the ovomucin molecules by electron microscopy revealed its linear character but also indicated a lower Mr than that obtained in the light-scattering experiments. By temperature-induced non-specific aggregation of an ovomucin solution containing other globular egg proteins, an attempt was made to find out what conditions are required for gel formation and to examine the quality of aggregation that is obtained under these conditions. Results show that the viscosity of the solution did not increase after heat treatment. Apparently, in the ovomucin gel, specific spatial organization of the ovomucin molecules is required for hydrogel formation.