OBJECTIVE For patients with diabetic ketoacidosis (DKA), arterial blood gas (BG) sampling for measurement of pH and bicarbonate has been considered an essential part of initial evaluation and monitoring of progress. There is growing evidence that venous values can be clinically acceptable alternatives to arterial measurements. This article summarizes the recent evidence regarding the validity of venous BG sampling in DKA. METHODS Medline search for the years 1995 to present, hand search of reference lists, search of on-line evidence-based medicine sites. RESULTS In patients with DKA the weighted average difference between arterial and venous pH was 0.02 pH units (95% limits of agreement -0.009 to +0.021 pH units) and between arterial and venous bicarbonate was -1.88 mEq/L. CONCLUSIONS There is reasonable evidence that venous and arterial pH have sufficient agreement as to be clinically interchangeable in patients with DKA who are haemodynamically stable and without respiratory failure. There is some evidence that venous and arterial bicarbonate also agree closely in DKA but this requires confirmation.