Fibril formation in mixtures of whey proteins upon heating at pH 2 was investigated. Fibrils were found to coexist with other structures, such as spherulites. These spherulites consist of radially oriented fibrils. At total protein concentrations above 6 wt %, transparent gels were formed. Changing the ratio between the various whey proteins did not affect this gelation concentration as long as β-lactoglobulin (β-lg) was present, suggesting that β-lg was dominant in the gelation. Pure α-lactalbumin and pure bovine serum albumin did not form fibrils, nor did they gel upon heating at pH 2 and 80 °C for up to 10 h. They did however induce a decrease in the β-lg concentration needed for gel formation upon heating at pH 2. Our results suggest that β-lg is the only fibril forming protein at the conditions used and that no mixed fibrils are formed. Keywords: Heat-induced aggregation; heat-set gelation; fibrils; whey proteins; β-lactoglobulin