The fatty acid composition of plasma cholesterol esters (CE), erythrocytes (RBC) and mature milk from seven lactating/women and their exclusively breastfed newborns, living on Dominica, were studied. Blood samples were taken from umbilical cord and mother at birth. A sample of breastmilk was collected on day 20-22 postpartum, together with a blood sample from the baby. At birth, cord blood plasma CE and RBC total long chain polyunsaturated fatty acid (LC-PUFA) contents were higher, and linoleic (18:2c, omega 6) and alpha-linolenic (18:3c, omega 3) acid contents lower, than in corresponding maternal compartments. Cord blood RBC LC-PUFA omega 3 content was lower and LC-PUFA omega 6 content higher than in maternal RBC. After birth, feeding with human milk led to a drop in LC-PUFA content in the plasma CE fraction, whereas RBC LC-PUFA content remained virtually constant. Current understanding of the origin and relative affinity of fatty acids incorporated in plasma CE and RBC suggests that RBC LC-PUFA content is a more reliable parameter for LC-PUFA status than plasma CE LC-PUFA content. The RBC LC-PUFA data suggest therefore that at birth the newborn has a lower LC-PUFA omega 3 status than the mother, and that this does not change during three weeks of exclusive breastfeeding.