Between April 1999 and March 2004, metabolic profile analyses were performed on individual blood samples from 35,506 dairy cattle in the uk. Assessment of the cows' energy status by the analysis of plasma samples for (β-hydroxybutyrate, glucose and non-esterified fatty acids showed that 70·4 per cent of the cows in early lactation (10 to 20 days calved), 57·1 per cent of the cows in mid-lactation (51 to 120 days calved) and 57·7 per cent of the dry cows within 10 days of their predicted calving date had one or more energy metabolites outside the optimum range; in addition, 16 per cent of the cows in early lactation, 5·6 per cent of those in mid-lactation and 20·5 per cent of the dry cows within 10 days of their predicted calving date had a low plasma urea nitrogen concentration, indicating poor intakes of effective rumen-degradable protein. Abnormalities in the concentrations of magnesium, inorganic phosphate, copper, selenium and iodine were relatively uncommon. The transitional period, particularly in late pregnancy, was commonly identified as a constraint on productivity. Nutritional problems were most commonly associated with poor feed intakes and poor feed management, rather than with the formulation of the rations.