The measurement oflactate is straightforward and reliable. The sampling is normal- ly dependable, although discrepancies between sample sites can occur if samples are drawn during other than steady state conditions or when blood flow to the site is low. Comparison of data between subjects should consider intra- and interindividu- al variation. Interpretation of the significance of blood or even a muscle lactate concentration is extremely difficult and neither can be assumed to reflect rates of lactate release or production. Lactate metabolism appears to be very significant in short-term, high- intensity work lasting a few seconds, but the exact role remains to be established. Blood lactate and the pulmonary aspects of anaerobic threshold are not necessarily causally related and the significance of anaerobic threshold as a metabolic measure remains obscure. There are numerous examples of changes in blood or muscle lac- tate independent of oxygen availability, and factors such as H+ concentration ap- pear to play an important, although undefined, role in regulating lactate production and/or release.