As Hartmann's solution is commonly used by anaesthetists, we surveyed a group of Part III FRCA candidates to establish their knowledge of its constituents and the purpose and metabolism of the lactate in solution. Of the 82 candidates surveyed only three (4%) accurately recorded the electrolytes and their concentrations in Hartmann's solution. Lactate was stated to be a source of bicarbonate by 52 (63%) and a source of glucose by 17 (21%). The descriptions of lactate metabolism were largely imprecise, none was complete and 24 (29%) of candidates offered no explanation. The constituents of Hartmann's solution and their concentrations are designed to match those of plasma, reducing ion and fluid shifts postinfusion. The lactate in Hartmann's solution is metabolised by both oxidation and gluconeogenesis, predominantly in the liver, and bicarbonate is generated by both processes over 1-2 h.