This thesis deals with some factors affecting the plasma lipids in apparently healthy persons, in patients with atherosclerotic arterial disease, and in two groups of subjects predisposed to atherosclerosis; namely, habitual cigarette-smokers and obese persons. It is in five main parts 1. A comparison of fasting plasma lipid concentrations in healthy and atherosclerotic subjects. 2. A comparison of fat tolerance tests in heathy and atherosclerotic subjects, 3. An examination of several aspects of gastric function alleged to influence fat tolerance; namely, the basal secretion, motility, and lipolytic ability of the stomach. 4. An investigation of the acute effects of cigarette-smoking on the plasma lipids and thrombotic tendency of the blood. 5. A study of the plasma lipid and other metabolic changes induced by therapeutic starvation in obese subjects.