In 1883, he embarked on another Royal Geographical Society expedition, this time to explore a route from the eastern coast of Africa to the northern shores of Lake Victoria. British Empire traders wanted a route that would avoid potentially hostile Maasai and German traders who were competing in the area. The expedition set out a few months behind the rival German expedition of Gustav A. Fischer. Thomson's leadership was again a success, demonstrating the feasibility of the route and making many important biological, geological, and ethnographic observations, though Thomson's attempt to climb Mount Kilimanjaro in a day failed. However, on the return journey, Thomson was gored by a buffalo and subsequently suffered from malaria and dysentery.