Milk fever is a disease of increasing importance. In dairy herds its incidence has doubled since 1950; today about 8 per cent of parturitions in Swedish dairy cattle are complicated by milk fever. At the same time, the clinical picture has changed and the effectiveness of calcium therapy has been markedly reduced. Thirty to 40 per cent of cows with milk fever need more than one treatment. These trends are obvious in Sweden and Norway and have been reported from many other parts of the world. However, there are also geographical and breed differences so that these figures might not be applicable under British conditions.