Objective: To compare the effects of valsartan and atenolol on sexual activity and plasma testosterone in newly diagnosed, previously untreated, essential hypertensive male subjects. Methods: One hundred and ten hypertensive men, aged 40-49 years, homogeneous for marital status and without any previous sexual dysfunction were randomly treated with valsartan 80 mg daily (o.d.) or atenolol 50 mg o.d. for 16 weeks according to a double-blind, parallel-arm study design. After 8 weeks the dose was doubled in the non-responders (diastolic blood pressure > 90 mmHg). Clinical evaluation was performed after 8 weeks and 16 weeks of treatment and included blood pressure and plasma testosterone measurements and the compilation of a questionnaire about sexual activity (sexual intercourse episodes/month). Results: Despite similar blood pressure lowering, atenolol significantly reduced sexual activity (from 6.0 sexual intercourse episodes/month to 4.2 sexual intercourse episodes/month, P < 0.01 vs placebo), whereas valsartan increased it, although not significantly (from 5.8 sexual intercourse episodes/month to 7.4 sexual intercourse episodes/month, P=0.058), compared with placebo, but significantly compared with the atenolol group (P < 0.05). Testosterone was reduced by atenolol (from 18.2 nmol/l to 13.8 nmol/l, P < 0.01 vs baseline) but was not affected by valsartan (from 17.6 nmol/l to 18.3 nmol/l). Conclusions: These results suggest that atenolol induces a worsening of sexual activity and a reduction of testosterone, whereas valsartan does not worsen sexual activity and does not change testosterone levels.