Clinical and laboratory examinations were carried out in a prospective study from 1978 to 1998 on 454 spontaneously diseased sheep of different breeds aged 2-8 years. Three groups of sheep were defined by plasma concentrations of 3-hydroxybutyrate (3-OHB) and calcium. 214 ewes suffered from ketosis (pregnancy toxaemia, 3-OHB > 1.6 mmol/l), 195 ewes and 5 rams suffered from hypocalcaemia (Ca < 2.0 mmol/l), and 40 ewes were sick with booth diseases simultaneously. Clinical findings differ only slightly in all three groups. In ketosis the time until the onset of clinical signs and the duration of the disease is somewhat longer, while locomotion disturbances are less severe than in hypocalcaemia and in the combination of both. In individual cases a differential diagnosis is not possible on the basis of clinical findings, and also acetonuria is not a reliable criterion. Therefore, a therapy is suggested to treat all three possible forms of disease: daily oral application of Na-propionate, Ca-lactate and K-chloride, and additional subcutanous injection of Ca-borogluconate, vitamin D3, alpha-Tocopherol and selenium at the beginning of the disease. Pathogenesis of both diseases are discussed, recommendations for feeding management are given.