The effect of cyclopropene fatty acids fed in saturated or unsaturated lipid diets on reproduction and lipid composition of progeny was determined in rats. Sterculia foetida oil (50% cyclopropene fatty acids) fed at 0.2% of the diet for three generations and 0.5% fed to first generation rats did not significantly affect breeding. Two percent S. foetida oil fed with 3% corn oil did not appreciably affect conception rate and litter size in the first litters, but reduced pup survival 36% in the first litters and 78% in the second litters. Replacement of the 3% corn oil with 3% animal fat in diet containing 2% S. foetida oil reduced litter rate from 87% to 7% in the first litter. Cyclopropene fatty acids were readily incorporated into the tissue and milk of females. Pups rapidly accumulated cyclopropene via milk from dams. Fetal tissue contained only 10% of the cyclopropene concentration of the females fed a diet containing 2% S. foetida oil and 3% corn oil; however, the level of fetal cyclopropene doubled when animal fat replaced corn oil in the diet. Unsaturated lipid in the diet enabled rats to cope with the effects of moderate levels of cyclopropene fatty acids, but the combination of cyclopropene in saturated lipid diets caused detrimental effects.