Introduction The aim was to examine how far the postpartum metabolism can be stabilized by oral supplementation with Vitamin B-12. Concentrations of Vitamin B-12 and cobalt, further metabolic parameters and erythrocyte measurements were examined from two to six days post partum (p.p.) to four weeks p.p. The morbidity rate was recorded during,. the first three months p.p. Materials and methods From four to six weeks ante parturn (a.p.) until calving, 65 Holstein Friesian (HF) cows were given a Vitamin B-12 supplement of 0.5 g Vitamin B-12 per cow and day in addition to their dry cow ration. Seventy-one HF cows without this supplement served as control group (CG). In addition to clinical controls, blood samples were taken for analysis of metabolic characteristics between the to sixth day p.p. and four to five weeks p. p. Results In the control group, 47.9% of the cows stayed healthy for the first three months p.p. In the experimental group (EG), the fraction of healthy cows was 60%. In the CG, 12.7% had a Retentio secundinarum and 40.8% a mastitis; in the experimental group the fractions were 21.5% and 26.2%. At two to six days p.p. the Vitamin B-12 concentration in the EG was significantly higher (320 pg/ml) than in the CG (224 pg/ml). The difference was still significant at four weeks p.p. The concentrations of Cobalt, NEFA, bilirubin and cholesterol as well as the creatine kinase activity did not differ significantly between the two groups. Erythrocyte counts and haemoglobin concentrations were significantly higher in the EG. Milk fat content (%) was significantly higher in the EG than in the CG (p=0.022); the milk yield did not differ significantly. Conclusion Significantly higher Vitamin B12 and haemoglobin concentrations, higher erythrocyte counts as well as lower morbidity rate show the positive effects of Vitamin-B(12)supplementation. There were no changes in the parameters of liver and energy metabolism or in the milk yield.