There he conducted research on guanine, xanthine, caffeine, and theobromine, and on the very toxic thallium oxides, which damaged his health severely. He moved to the University of Würzburg in 1870, but his first semester was interrupted by the Franco-Prussian War of 1870–1871. Strecker became an officer during the war and returned to the university after it, where he started his last semester.