Objectives Testosterone replacement therapy in hypogonadal men relieves symptoms and restores serum testosterone levels to the physiological range. In this study, we assessed the safety, pharmacokinetics, and efficacy of the 2% formulation of testosterone topical solution applied daily to the axillae. Design and Patients An open-label trial was conducted in testosterone-deficient men who started on a daily dose of 60 mg of testosterone. Dose was adjusted on Days 45 and 90 when necessary to maintain serum testosterone levels within the physiological range (10·41-36·44 nmol/l) based on average serum testosterone levels on Days 15 and 60, respectively. Sexual function and mood changes were assessed by the Psychosexual Daily Questionnaire (PDQ) for the 7 days preceding visits at Days 1, 15, 60, and 120; and quality of life by SF-36 questionnaire on Days 1, 60, and 120. Safety parameters, laboratory tests, and adverse events were collected at each visit. Results Among the Completer Set (135 study completers and 3 patients who discontinued due to adverse events), 76·1% (Days 15/16), 84·8% (Days 60/61), and 84·1% (Days 120/121) had an average total testosterone level between 10·41- 36·44 nmol/l. PDQ scores increased significantly from baseline to 120 days of treatment (p <0·0001). Significant improvement was observed in the physical (p <0·05) and mental (p <0·0001) components of the SF-36 after120 days of treatment. Adverse events reported in >2% of the 155 subjects who received ≥ 1 dose were application site irritation (7·1%), application site erythema (5·2%), headache (5·2%), increased hematocrit (3.9%), nasopharyngitis (3·9%), diarrhea (2·6%), and vomiting (2·6%). Conclusions These results indicate that once-daily application of the testosterone topical solution 2% to the axillae is a safe and effective treatment for androgen replacement in hypogonadal men.