It is well known that -Lactoglobulin in solutions at neutral pH underwent a heat-induced denaturation and aggregation, and that -Lactoglobulin solutions at large concentrations gel. This has a large interest in the food industry. Less is done on the gelation of -Lactoglobulin (or whey proteins containing -Lactoglobulin as their major protein) at alkaline pH. Exposure of the protein at pH > 6 produces 2 successive transitions, a first reversible one, between pH 6 and 8, and a second irreversible one, between pH 9 and 13, that slowly leads to partially unfolded monomers of -Lactoglobulin, a decrease in rigid tertiary -Lactoglobulin structure, exposure of buried SH groups and finally to -Lactoglobulin polymerisation, probably by thiol oxidation. We have studied the gelation of whey protein isolate or -Lactoglobulin at pH 9.5 by rheological measurements at 4 and 20°C, as a function of the protein concentration. Protein polymerisation is faster at higher protein concentration and at 4°C than at 20°C. Using N-ethyl maleimide allows to confirm the role of SH groups in the gelation. The results improve our understanding of -Lactoglobulin polymerisation at alkaline pH values. They also could be applied in food processes, either to produce aggregates for increasing the texture of food matrix, or to prevent aggregation, for instance during the production of polymer-free whey protein powders or during the cleaning of membranes used in tangential filtration processes.