The influence of different factors on variations in the concentrations of total phospholipids and high-density-lipoprotein (HDL) phospholipids in plasma was studied in a presumably healthy population of 2000 subjects, four to 70 years old. Age is the major factor associated with variation of total phospholipids. In females, this is due in part to age-related changes in hormonal status. The use of oral contraceptives affects only HDL phospholipid values. Use of tobacco does not influence plasma phospholipid values, but alcohol consumption increases values for both total and HDL phospholipids. We propose reference intervals for total plasma phospholipids and HDL phospholipids, adjusted for age and sex. Screening for lipid status can now include determinations of phospholipids as well as cholesterol and triglycerides.