In this article we examine how a leading Israeli hospital gradually became a large biomedical research facility, resembling a huge laboratory. For Chaim Sheba (1908-1971), the founder and first director of Tel-Hashomer Hospital, the massive immigration to Israel in the 1950s was a unique opportunity for research of diverse human populations, especially Jews who had arrived to Israel from Asia and Africa. The paper focuses on the way research and medical practices were integrated and their boundaries blurred, and studies the conditions under which an entire hospital became a research field. Using the case of one of Israel’s prominent medical institutes, we explore and expand upon the idea of “the hospital as a laboratory,” arguing that, for Sheba, it was not only the hospital but the entire country that functioned as a great research site—a vast laboratory that “had no walls.”