A total of 351 single-suckled beef calves were blood sampled at twice-weekly intervals for the first two and a half weeks of life. Twenty three of them died, 13 of a syndrome characterised by acute collapse and 10 of diarrhoea which had persisted for several days before death. Those which died acutely showed a sudden terminal rise in blood levels of potassium, magnesium, inorganic phosphate and total protein. Those which died after several days of diarrhoea showed a more gradual increase in blood chloride and urea concentrations and in packed cell volume values. It is suggested that these changes indicate a difference in the pathogenesis of the two situations. Calves which died had lower blood glucose levels before the onset of clinical signs than those which survived. It is suggested that this may have been a contributory factor in their mortality.