SCHAFFER solution (formalin-methanol in NaPh buffer) is a specialized in vitro diagnostic agent used primarily in pathology. Its main application is in the fixation of tissue preparations to preserve tissue structure and prepare specimens for subsequent histological examination. Formaldehyde and methanol in the solution react with proteins and nucleic acids in the cells, stabilizing them and preventing their decomposition. The included NaPh buffer ensures the optimal pH environment during this process and thus improves the quality of fixation. Glucose monohydrate serves as a protective substance to protect cells from the potentially harmful effects of fixation. After application of this solution, the morphological structure of the tissue is preserved, allowing reliable and detailed histological and cytological analyses. The SCHAFFER solution thus contributes to improving diagnostic accuracy.