The hypothesis that mandibular bone-strain patterns are a good indicator of molar bite-force patterns in M. fascicularis during mastication was tested by determining the relationship between mandibular bone-strain patterns and bite-force patterns during isometric biting. Bone-strain patterns were determined using rosette strain gauges bonded to mandibular cortical bone below the roots of the M2 during isometric binding on a transducer along the M1-M2 region. The effects of rosette position on bone-strain patterns during mastication was determined by comparing bone-strain patterns recorded from two different rosettes; one bonded below the roots of the M2 and the other below the roots of the M3. The data from the two experimental sets support the hypothesis that bone-strain patterns along the working side of the mandible are a good indicator of bite-force patterns during the power stroke. The relationship between bone-strain patterns and bite-force patterns was not perfect and the two principal strains were not of equal value. In general, principal compression was a better indicator of bite force than principal tension.