The purpose of this study was firstly, to determine the level of agreement between the Lactate Pro and Analox GM7 for the measurement of blood lactate, and secondly, to examine whether these analysers may be used interchangeably to identify lactate parameters routinely used in the physiological assessment of athletes. Twenty well-trained male cyclists performed an incremental cycle ergometry test; duplicate blood samples were taken simultaneously throughout the test for lactate determination using the two analysers. Power output and heart rate at LT, LT1, 2 mmol · L-1, and 4 mmol · L-1 were calculated from the lactate values obtained from the two analysers. There was a strong linear relationship between the two analysers (Lactate Pro = 1.4541 × Analox GM7-0.1287; R2 = 0.969, p < 0.001; SEE = 0.704) though the Lactate Pro overestimated blood lactate when compared to the Analox GM7; 95% ratio limits of agreement (Lactate Pro/Analox GM7) were 1.40 ×/÷ 1.35. Differences were found between analysers for power output and heart rate at LT1 (p < 0.01), 2 mmol · L-1 (p < 0.001), and 4 mmol · L-1 (p < 0.001); no differences were found between analysers for power output or heart rate at LT. In conclusion, the average difference in blood lactate concentration measured by the Lactate Pro and the Analox GM7 was 40%, with 95% of measures differing by between 4% and 89%. This poor level of agreement and the significant differences between the two analysers in power output and heart rate associated with a number of lactate parameters indicate that these analysers should not be used interchangeably.