In the past few years several portable blood lactate analyzer have been available to use in athletes. Even though the increased practicality and portability of these new devices is hard to beat, only few studies have compared their performance with laboratory-based analyzers such as the Yellow Spring Instruments (YSI). Moreover, studies comparing Lactate Plus with YSI or other laboratory-based analyzers are scarce or used a limited number of samples, respectively. PURPOSE: To compare whole blood lactate values between YSI 1500 Sports and Lactate Plus in a wide range of lactate values (0.75 - 18.50 mmol/L) and to determine agreement between both instruments. METHODS: 76 swimmers were tested during field incremental and steady-state exercise tests or post-race at official meetings. Blood sample collection was performed from the earlobe using a heparinized capillary and following published guidelines to obtain arterialized blood. Only one capillary of blood (∼50 μL) was collected per sample, 25 μL and 0.7 μL were used for YSI and Lactate Plus analyses, respectively. Linear correlations between YSI and Lactate Pro and Bland-Altman agreement analyses were performed using all the samples and dividing the samples in low (0.75 - 10 mmol/L) and high (> 10 mmol/L) lactate levels. RESULTS: 310 blood samples, 179 low and 131 high, were obtained from the subjects and are included in the present analysis. Significant correlations were observed on all three analyses (ALL: YSI=0.613 + 0.852*Lactate Plus; r=0.977, p<0.001; LOW: YSI=0.458 + 0.871*Lactate Plus; r=0.965, p<0.001; HIGH: YSI=3.997 + 0.628*Lactate Plus; r=0.737, p<0.001). Bland-Altman analyses showed a good agreement when using 95% CI (ALL: 92.9 % of the sample within [-2.14 - 2.14 mmol/L] range; LOW: 94.4 % of the sample within [-1.33 - 1.33 mmo/L] range; HIGH: 94.7 % of the sample within [-2.70 - 2.70 mmol/L] range). CONCLUSIONS: The results of the present study show significant correlations between YSI 1500 Sports and Lactate Plus lactate analyzers. Moreover, the Bland-Altman analyses show a good agreement between both instruments. Based on this study’s findings, it could be appropriate to surrogate or replace YSI measurements with Lactate Plus values. However, for samples above 10 mmol/L, the 95% CI is too broad, which could increase reading error.