A trial was conducted to investigate the response of prepartum dairy cows to reducing the level of dietary cation-anion balance by measuring the concentration of plasma Ca, P, Mg and hydroxy proline, the apparent absorption of Ca, P and Mg and the incidence of milk fever. Twenty prepartum Holstein cows were randomly allocated to four dietary treatments designated control, diets 1, 2 and 3, with cation-anion balances [(Na + K) – (Cl + S)] of + 394, + 121, + 105 and + 62 meq kg−1 dietary dry matter (DM), respectively. Diets containing 1.38% Ca and 0.76% P (dry basis) were offered from day 45 prepartum to day 2 postpartum. Reducing the level of dietary cation-anion balance decreased the severity of the decline of plasma Ca during the periparturient period and delayed the time of observing the lowest concentration of plasma Ca. Strong negative correlations were observed during the periparturient period, particularly at parturition, between dietary cation-anion intake and the concentrations of plasma Ca and P. Apparent absorption of minerals was not influenced by dietary treatment from day 24 to day 21 prepartum. However, apparent absorption of Ca was reduced in cows fed diets 2 and 3 compared to cows fed the control diet and apparent absorption of Mg was reduced in cows fed diets 1, 2 and 3 compared to cows fed the control diet from day 7 prepartum until day 1 postpartum. Apparent absorption of phosphorus was not influenced by treatment at either time. Plasma levels of hydroxyproline were higher in cows fed diets 2 and 3 than in those fed diet 1 and the control diet from day 2 prepartum to day 1 postpartum. Results showed that reducing the level of dietary cation-anion balance influenced the concentration of plasma calcium, its apparent absorption and its resorption from bone. These effects were most accentuated during the periparturient period and may be beneficial in the prevention of milk fever. Key words: Milk fever, dairy cows, dietary anions and cations, parturient paresis