The purpose of this study was to determine the anaerobic threshold of children by the analysis of saliva collected during field tests. A group of 25 children (mean age, 10.5 years) performed an incremental exercise test on a track, consisting of 4-min stages at increasing running velocities. Before each test (at rest) and at the end of each stage, both blood (via finger pricks) and saliva samples (for measurement of salivary concentrations of Na+ and Cl-) were collected to determine lactate threshold (Thla-) and saliva threshold (Thsa), respectively. There were no significant differences between values of Thla- and Thsa when expressed either as running velocity [mean Thla-, 10.73 (SD 1.96) km.h-1; mean Thsa, 10.89 (SD 1.69) km.h-1)] or heart rate [Thla-, 182(SD 14) beats. min-1 Thsa 183 (SD 11) beats.min-1]. In addition, correlations between Thsa and Thla were high, when both values were expressed as running velocity in kilometres per hour (r = 0.89; P < 0.001), or heart rate in beats per minute (r = 0.90; p < 0.001). In conclusion, these findings suggested that saliva analysis would be a valid method for anaerobic threshold determination in field tests.