The feeding of low protein diets to pregnant rats is known to programme hypertension in their offspring though a glucocorticoid-dependent mechanism. To establish whether diets of differing fatty acid composition could produce the same effects, or modulate the effects of a low protein diet, pregnant rats were fed 1 of 4 different diets. Control animals were fed an 18% casein:corn oil (18 + Corn) diet, while experimental groups were fed 18% casein:coconut oil (18 + Coco), 9% casein:corn oil (9 + Corn) or 9% casein:coconut oil (9 + Coco). Feeding of coconut oil diets significantly reduced weight gain of the rats, an effect attributable to a lower food intake. Despite this, reproductive performance of the rats was not compromised. While pups of the 9 + Corn group were of normal birthweight, the dams in the 18 + Coco and 9 + Coco groups gave birth to pups of significantly lower weight. At 7 weeks of age male and female pups exposed to the 9 + Corn diet in utero had significantly elevated systolic blood pressure. Males exposed to the 9 + Coco and 18 + Coco diets also had higher blood pressures than control animals, but the effect was not observed in females. Female rats exposed to the three experimental diets in utero had enlarged hearts, relative to controls and the same effect of maternal diet was observed in male rats exposed to the 9 + Coco and 18 + Coco diets. Effects of maternal diet upon liver size were also noted in males exposed to 18 + Coco and 9 + Corn diets (smaller livers). Males exposed to 9 + Corn had smaller lungs than control rats, whilst the rats from the 9 + Coco group had significantly enlarged lungs. In rats exposed to the 9 + Corn diet in utero there was evidence of increased glucocorticoid action in both liver and hypothalamus, where activities of corticosteroid inducible enzymes were elevated. There was no evidence of a role for glucocorticoids in programming the hypertension of male rats exposed to high saturated fat diets in utero. The data would suggest that high saturated fatty acid, or low linoleic acid intake in pregnancy may programme hypertension in the fetal rat. This effect of maternal diet occurs through a mechanism different to that initiated by protein restriction and is sex specific.