INTRODUCTION: Quantitative studies of hand motor strength are limited by devices that measure grip and pinch strength. A complete quantitative analysis of pure thumb abduction and adduction motor strength in the normal population has not been done. Isolated analysis of this motor function can be important in the preoperative and postoperative evaluation as well as the long term management of patients with disorders that can result in weakness of these specific muscles. METHODS: Volunteers with no history of upper extremity disoders or surgery (n=600) between the ages of ten and seventy were tested. This group consisted of 294 males and 306 females, which were then stratified according to age and weight. Hand dominance and the value of mid range grip strength was measured. Thumb abduction and adduction were measured using a new device designed for this task. This TAAM (Thumb Abduction Adduction Measuring) device consists of a slot to immobilize the palm and a pressure sensitive ring for the thumb. Force is measured through a 50 pound load cell which is accurate to 0.1 pound. Values for abduction and adduction strength were recorded at the 30 degree, 45 degree, and 60 degree of thumb abduction. RESULTS: Males at the 45 degree position right thumbs exhibited an average strength of 4.3+/-1.7 pounds abduction and adduction strength of 17.0+/-4.5 pounds. For females, abduction was 2.3+/-0.9 pounds and adduction was 14.3+/-3.8 pounds at the 45 degree position. There was no statistical significance in abduction or adduction strength between dominant and non dominant hands. At higher degrees of thumb abduction, the strength of abduction decreased while adduction strength increased. The ratio of adduction and abduction strength with age was poor for both males and females. The correletion with weight was better and significant with grip strength. CONCLUSIONS: We found the TAAM device was easy to use and required a small amount of time to complete. Studies that quantify the relative contribution of median and ulnar innervation in patients with carpal tunnel syndrome and ulnar neuropathy are underway. As this is first device to specifically measure pure thumb abduction and adduction strength, studying the natural history of these disorders might allow us to determine a strength loss threshold to better guide when operative release maybe strongly indicated.