Dr Richard Schoub of London wrote in connection with the article by Dr Barrie Phypers and Dr Tom Pierce on lactate physiology in health and disease (CEACCP 2006; 6: 128 ­32). He congratulates the authors but highlights the concept of lactate clearance in the critically ill. He stated `Most intensivists agree that the presence of a raised lactate level in the septic patient denotes a more severe underlying process, and therefore worse prognosis (as discussed). However even this point is not universally accepted.1 Rather than a single lactate value, it is the trend in the lactate values, in particular the ability of the body to clear lactate, that provides the best indication of severity of disease, adequacy of treatment and likelihood of survival. The prognostic significance of lactate clearance was already described by Bakker in what he called `lac-time'2 and reinforced as one of the greatest determinants of survival in sepsis more recently by Nguyen et al.3 A falling lactate (ie short lac-time) provides good evidence of improvement of both circulatory function and cellular metabolism (ie less lactate production) as well as hepatic recovery (ie greater lactate metabolism). It is therefore unsurprising that measuring lactate clearance is of such great importance in the management of critically ill patients' Drs Phypers and Pierce replied `Dr Schoub has drawn to our attention to `lactime' and lactate clearance as predictors of survival. Bakker et al.2 defined lactime as the time during which the lactate concentration is above 2 mmol/l, and was found to...