Purpose: To identify differences in heart rate (HR) and concentration of blood lactate ([La]) relationships between laboratory- and field-based skate-roller-skiing tests. Methods: Fourteen world-class biathletes (8 women, 6 men) completed a laboratory- and field-based roller-skiing test using the skate technique. The laboratory-based test comprised 5 to 7 submaximal steps at a fixed incline and speed on a roller-skiing treadmill. The field-based test comprised 5 steps on a course where the final hill was designed to mimic the conditions of the laboratory test. HR and [La] were measured for each step. The HR associated with 2 mmol·L⁻¹ (HR_@2 mmol) and 4 mmol·L⁻¹ (HR_@4 mmol) of [La] was calculated using an interpolation method. A 1-way analysis of variance and Bland–Altman analyses with 95% limits of agreement (LoA) were used to determine if test type influenced HR_@2 mmol or HR_@4 mmol. A second-order polynomial was fitted to group-level data to highlight the HR–[La] relationships for laboratory- and field-based tests. Results: HR_@2 mmol was lower for field tests than for laboratory tests (mean bias: 1.9%HR_max; 95% LoA: −4.5 to +8.3%HR_max; P < .001). HR_@4 mmol was also lower for field tests compared to laboratory tests (mean bias: 2.4%HR_max; 95% LoA: −1.2 to +6.0%HR_max; P < .001). On the group level, the lactate threshold occurred at a lower HR during roller skiing in the field compared to the laboratory. Conclusions: The findings from this study confirm that for a given HR, [La] was greater in field- compared with laboratory-based conditions. These results might have implications for how coaches define training-intensity “zones” during skate roller skiing based on laboratory tests.