Muscle tone (stiffness/hardness) or muscle compliance changes during muscle contraction. The purposes of this study were to assess the intrarater and interrater reliabilities of the Myotonometer®, electronic device that quantifies muscle tone. Two raters used the Myotonometer to assess the right bicep brachia and quadriceps muscles of 30 voluntary persons without any orthopedic or neurological problems (age range, 18~21 yrs). Muscles were measured in a relaxed state and during brief sustained voluntary maximal isometric contraction. Intrarater correlation coefficients were calculated for each muscle and for each condition (relaxed and contracted). Intrarater reliabilities (intraclass correlation coefficients, ICCs) ranged from .778 to .954, relaxed, biceps brachia), .926 to .963 (contracted, biceps brachia), .935 to .990 (relaxed, quadriceps) and .679 to .952(contracted, quadriceps). Interrater reliabilities ranged from .652 to .790 (relaxed, biceps brachii), .813 to .907 (contracted, biceps brachii), .831 to .950 (relaxed, quadriceps) and .849 to .937 (contracted, quadriceps). Myotonometer measurements had high to very high intrarater and interrater reliability for measurements of the biceps brachia and quadriceps muscles.