The (R,S)-1,3-butanediol-acetoacetate monoesters and diester are nonionized sodium-free precursors of ketone bodies (beta-hydroxybutyrate and acetoacetate). They represent a convenient form of ketone body administration for parenteral and enteral nutrition. We have studied the metabolism of the esters in the conscious pig, an animal in which ketogenesis is congenitally impaired. Some pigs were infused for 3 h, intravenously or intragastrically, with the esters or with (R,S)-1,3-butanediol at 30% of the hourly caloric requirement. Other pigs were given intragastric boluses of esters or of (R,S)-1,3-butanediol at 15% of the daily caloric requirement. Our data show that continuous infusion of the esters at 30% of the caloric requirement leads to low concentrations of (R,S)-1,3-butanediol (0.1 mM) and total ketone bodies (0.5 mM). In pigs given intragastric boluses of esters at 15% of the daily caloric requirement, concentrations of (R,S)-1,3-butanediol and total ketone bodies peaked briefly at 2-3 and 5 mM, respectively. No deleterious side effects were observed in any group, including no hypoglycemia and no acidosis. Thus the (R,S)-1,3-butanediol acetoacetate esters appears to be well utilized as a nutrient by the pig despite its impaired ketogenesis.