Using a modified skin surface lipid measuring instrument. the Meibometer, the amounts of meibomian lipid on the lid margins (the casual levels) of 421 subjects aged 1 to 94 years were measured. The lowest levels were found in children younger than 14 years (means±S.E.: males = 1.48±0.17, females = 1.53±0.17μg lipid/mm2lid margin surface) and rose with age, the highest levels being found in males aged 60–69 years (mean±S.E. = 3.26±0.18μg lipid/mm2lid margin surface). Male levels were higher than females in the 20–29 years age group but male and female levels became indistinguishable above the age of 50. These age- and sex-related changes differed markedly from those seen in skin surface lipid levels. The age-related changes in the casual levels of lid lipids remain unexplained although an endocrinological mechanism modified by morphological factors is considered.