The Soviet–German Syphilis Expedition was a joint Soviet and German expedition that took place in 1928. It comprised eight medical researchers from each country and its purpose was to investigate endemic syphilis in the Kul’skoe region of the Buryat-Mongolian Autonomous Republic in Siberia and to determine the efficacy of the anti-syphilis drug Salvarsan. The expedition concluded, contrary to expectations, that although affected by poor sanitation and lifestyle, the spread of syphilis in the area was caused primarily by sexual activity.