Choline is an important nutrient that is actively transported from mother to fetus across the placenta and from mother to infant across the mammary gland. Thus, pregnancy and lactation are times when dietary requirements for choline may be increased. Pregnant rats eating AIN-76A diet (with and without choline) for 6 d (d 12-18 gestation) were compared with nonmated female and male rats eating the same diets. Similarly, lactating rats were compared with nonmated female rats, both groups eating these same diets for 25 d (gestation d 12-postpartum d 15). We measured choline and choline metabolites in livers on the last day of feeding. Nonmated female rats, eating the control diet, had higher hepatic choline metabolites concentrations than did male rats (choline, 98%; betaine, 96%; and phosphorylcholine, 55% higher), pregnant rats (phosphorylcholine, 47%; and betaine, 42% higher) or lactating rats (phosphorylcholine, 49%; phosphatidylcholine, 37%; and betaine, 273% higher). We found that nonmated females eating a choline deficient diet had only a modest diminution (33%) of the labile choline metabolite PCho in liver, compared with similar rats eating a control diet. When compared with similar rats fed a choline-adequate diet, pregnant rats fed a choline-deficient diet had significantly great diminution of hepatic phosphorylcholine (83% lower) than did nonmated females. Liver phosphorylcholine was only 12% lower than in controls in nonmated females fed the deficient diet for the same 25-d period. Lactating rats were the most sensitive to choline deficiency, with liver phosphorylcholine 88% lower than in similar rats fed control diet.(ABSTRACT TRUNCATED AT 250 WORDS)