A new mucoadhesive testosterone buccal system (Striant), 30 mg testosterone (T), was applied twice daily in 82 hypogonadal men for 3 months. Serum T, free T, and 5alpha-dihydrotestosterone were measured during this period. T pharmacokinetics were determined from the data obtained during a 24-h sampling at wk 12. Physiological mean serum T concentrations were steady and consistently maintained. The mean percentage of time over a 24-h period that total serum T concentrations were above the lower limit of adult male range was 80.1%. During treatment, mean serum 5alpha-dihydrotestosterone, free T, and estradiol concentrations paralleled serum T. T pharmacokinetics were not significantly affected by body mass index, age, food or beverage, gum abnormalities, or medications known to cause dry mouth. Gum-related adverse events occurred in 16.3% of subjects. Except for three subjects, the gum adverse effects occurred early during treatment, did not cause interruption of treatment, and resolved rapidly and completely. The T buccal system is a novel T formulation that offers a safe, effective, and convenient alternative to existing formulations for physiological T replacement therapy in hypogonadal men.