With this new method, protrusive mandibular force was studied in a homogeneous group of 69 children with similar occlusions. Maximum protrusive force ranged from 18.5 to 160 N (mean +/- SD = 81.3+/-31.6 N). Maximum protrusive force was significantly higher in males (90.7+/-30.2 N) than females (66.6+/-28.6 N) while fatigue time was not significantly different between the two groups (70.6+/-38.5 s for males and 65.1+/-33.6 s for females). Although protrusive force was stable in each session, it varied considerably between different experimental days within the same individual. No statistically significant correlation was found between maximum protrusive force and age, skeletal maturity, height, weight, overjet, maxillomandibular relation, facial height, facial widths or facial proportions.