Lab investigations can be an important part of the evaluation of a patient's health status. Whether the dentist orders tests personally or refers the patient to a physician for testing, the dentist should be familiar with indications for clinical laboratory testing as well as what tests measure, and what abnormal results mean. Clinical chemistry is concerned with the diagnosis and monitoring of disease by measuring the concentration of chemicals, principally in blood and in urine. Hematology is concerned with the investigation and monitoring of diseases which affect the number, size and appearance of the cellular or formed elements of blood. Histopathology and Cytopathology is concerned with the diagnosis of disease by microscopical examination of tissue samples. Immunology is concerned principally with blood testing for the diagnosis of autoimmune diseases. Caries detection also plays an important role. The earliest is the diagnosis of the oral cancer, best is the prognosis of the cancer. This book highlights the lab investigations in dentistry with which a dentist comes across in day to day basis.