The metabolic effect of infusing 1.0-1.5 litre of Hartmann's solution to normal subjects and those with maturity onset diabetes has been studied during surgery. It was found that the use of Hartmann's solution after operation was associated with a 7.5 mmol litre-u increase in plasm glucose concentration compared with an increase of 2.1 mmol litre-1 in diabetic patients who received no i.v. fluids. In non-diabetic subjects who received Hartmann's solution the increase was 2.5 mmol litre-1. It is suggested that Hartmann's solution may be metabolically disadvantageous in diabetic patients.