This presentation attempts to examine some ways medical knowledge was brought into practices, and addresses its implications. Relying not just on categorical medical texts in general but rather on medical case writings, I inquire into how doctors incorporated their practice-based knowledge with text-based theories—with what attitudes doctors mobilized medical knowledge and in what ways they made diagnoses and composed prescriptions—in 18th and 19th century Korea. Exploration of four medical case writings under our investigation leads to the following: Active in the early 18th century, Yi Suki shows that he practiced medicine, while sheltering himself under the veil of antecedents’ works, in accordance with the received textbook-based medical knowledge and tried to confirm the efficacy of the age-old medical knowledge. He deployed ready-made-in-the-textbook formulas with minor additions of bencao drugs to adjust the details; Chang Taekyŏng, a middle-19th-century doctor, shows that he had great command of the received medical knowledge and utilized the literary and artistic apparatus to present himself to the readers in general; In contrast, Ŭn Suryong, in the middle 19th century, reveals the tension between theoretical and empirical knowledge. Drawing a line at the received textbook-based medical knowledge, especially at the ready-made formulas, Ŭn Suryong crafted prescriptions himself without recourse to the received drug formulas in dealing with down-to-earth diseases; Late in the 19th century, Yi Chema, keeping himself at a distance from ancient medical textbooks, manifests his intention to reconfigure or reconstruct East Asian Medicine based on his own recognition of human body and diseases. This distance-keeping attitude toward predecessors’ knowledge naturally results in the codifications of new drug formulas to complement East Asian Medicine, completing his own medical system. Not just leaving theses features as peculiar instances but putting these cases in the spatiotemporal context, we could say something more: In 18th century, a doctor showed a process in which the received medical knowledge was adapted and internalized in the field of practices, which arguably reflects his being connected to the metropolis-based bureaucratic expertise network; in 19th century, noticeably in the provincial regions away from the official network, some doctors began to make their own ideas and experiences into working knowledge, consequently speaking for themselves.