The metabolism of millimolar concentrations of R- or S-1,3-butanediol has been studied in perfused livers from fed and starved rats. Protocols were designed to measure in the same experiment (i) uptake of the diol, (ii) the contribution of the diol to ketogenesis, (iii) the contribution of the diol to total fatty acid plus sterol synthesis, and (iv) conversion of S-1,3-butanediol into S-3-hydroxybutyrate. Our data show that R- and S-1,3-butanediol are taken up by the liver at the same rate. Most of the metabolism of R-1,3-butanediol is accounted for by conversion to the physiological ketone bodies R-3-hydroxybutyrate and acetoacetate. Only 29-38% of S-1,3-butanediol uptake is accounted for by conversion into physiological ketone bodies. The balance of S-1,3-butanediol metabolism is conversion to S-3-hydroxybutyrate, lipids and CO2.