Terazosin selectively antagonises alpha 1-adrenoceptor-mediated contraction of the prostate, prostatic capsule, proximal urethra and bladder base, and consequently reduces urethral pressure, bladder outlet resistance and urinary symptoms associated with symptomatic benign prostatic hyperplasia. The efficacy of terazosin is reflected in increases in peak urinary flow rate, and reductions in obstructive and irritative symptom scores compared with placebo, and reductions in residual urinary volume from baseline. Clinical improvements begin to occur within 2 weeks and have been sustained for up to 2 years. The most marked treatment effects tend to occur in patients with more severe pretreatment urinary flow abnormalities. The relatively long duration of action of terazosin, allowing once-daily administration, offers a potential clinical advantage over other alpha 1-adrenoceptor antagonists although formal compliance studies have not been reported. Terazosin is generally well tolerated, but caution is recommended at treatment initiation and when dosage adjustments are made due to an increased risk of postural hypotension and related adverse effects at these times; such a risk has also been observed with several other alpha 1-adrenoceptor antagonists. Although publication of clinical trial results with terazosin is still evolving, this drug shows promise in the treatment of patients with mild to moderate symptomatic benign prostatic hyperplasia for whom surgery is not absolutely indicated. Terazosin also shows promise as a nonsurgical treatment alternative in patients with severe symptoms who are unfit for surgery and also in those who are on long waiting lists for surgery.