This study aimed to determine the stability of lactate concentration in blood samples preserved and stored using methods practical for field testing and experimental applications. Whole blood microsamples were obtained from venous samples drawn from 10 healthy subjects following bouts of moderate (approximately 5 mmol x l(-1), n = 12), or intense (approximately 10 mmol x l(-1), n = 12), treadmill exercise. Samples were analysed fresh (2 x 25 microl), or placed in preservative-containing tubes (12 x 75 microl) and analysed directly, or after storage at room temperature (RT) or 4 degrees C, for 1 h, 18 h, 2 d, 3 d or 7 d, or at -20 degrees C for 7 d. In comparison to preserved samples assayed directly after collection, lactate levels in all RT samples had declined significantly, whereas the 4 degrees C samples had not changed, by 2 d post-collection. After 7 d of refrigeration, the absolute value of the difference from lactate levels in samples measured after collection (mean +/- SD) was 0.38 +/- 0.34 mmol x l(-1), or 5.3 +/- 4.3%; with freezing, this difference was 0.27 +/- 0.27 mmol x l(-1), or 3.6 +/- 3.0%. These differences were less than the daily variation in the analyser readings of a 10 mmol x l(-1) standard, indicating that the blood preservation and storage methods identified herein are suitable for use during exercise testing.