Skin surface lipid levels in forty-five newborn babies and 193 infants aged less than 12 months were determined by an optical density method, using samples collected on ground glass. Although there was a wide individual range, sebum levels in the first week of life were very high, and were of the same magnitude as in adults. Females displayed a different pattern of sebum excretion from males. On the first day of life, the levels in females were lower than in the males but a large increase took place between the 3rd and 6th day, followed by a fall, bringing the level below that of the males. At 6 months the levels were low in both sexes. These findings suggest that there is a strong stimulation of sebum secretion before birth which probably stops at or soon after birth. Androgen may be involved in this stimulation and the probable role of dehydroepiandrosterone (DHEA) is discussed. Very few studies have been carried out on sebum secretion in newborn children. Emanuel (1936) was the first to demonstrate that the sebum level in newborn babies can be nearly as high as in adults. The levels then gradually decline to settle at a very low baseline until puberty. Since this study, our knowledge has remained elementary, in spite of repeated allusions to a seborrhoeic pathology in the newborn. This shortcoming is probably due to the fact that the techniques available were either dangerous for the child (i.e., the ether cup method used by Emanuel (1936)), or difficult and lengthy (i.e. the extraction on filter paper used by Strauss & Pochi (1961) and Cunliffe & Shuster (1969)). The Schaefer & Kuhn-Bussius (1970) photometric method, being both harmless and quick, is free from these drawbacks and enables sebum secretion to be measured at birth.