SummaryIn 10 male and 10 female adults jaw movements and muscle activity were monitored during chewing. Subjects had a Class I occlusion and fluent unrestricted jaw movements; none exhibited signs or symptoms of craniomandibular disorders. Recordings were made on two occasions separated by 2 weeks. Within each recording session the subjects carried out a number of tasks under direction, including eating nuts and gum. The jaw movements were monitored with a Sirognathograph® which had been interfaced to a computer for data logging and analysis.A computer program identified each chewing stroke and after scrutiny a data base was constructed of measurements from a subset of 4447 suitable strokes. Mean values of 10 parameters selected to describe jaw movements during chewing were entered into ananova. This indicated that the major contribution to variance was due to the subject from whom the data was recorded. This intersubject variability is well known, but can its separation from the other contributions to the variation within the data be assessed? To provide an estimate of the spread of data the variance for each parameter was calculated, transformed and these values entered into an analysis of variance.All subject differed significantly in their chewing movements from one another. But 15 of the 20 subjects showed a greater degree of consistency than the other five: they exhibited good inter‐ and intra‐recording reproducibility. The food being eaten made a major contribution to the variability. The timing of the chewing strokes was also more consistent than the dimensions of the chewing enve