This double-blind, randomized study was aimed at evaluating comparatively, in postmenopausal women, the activity of a standardized soy extract (SOYSELECT) and placebo when given alone or in combination with conjugated equine estrogens (CEE) on early climacteric symptoms. Lipid profile, pituitary hormones, osteocalcin and endothelin levels, and vaginal and endometrial parameters were also evaluated. Participants in the control group were given placebo, and participants in the treated group were given 400 mg/day of a standardized soy extract, corresponding to 50 mg/daily of isoflavones. After 6 weeks of treatment, CEE was also then given to each participant at a dose of 0.625 mg/day for 4 weeks. At the end of this period, soy and placebo treatment were suspended, and, until the end of the study (week 12), participants were administered 10 mg/day of medroxyprogesterone acetate in association with CEE (0.625 mg/day). When compared with pretreatment data, on week 6 of the study, a significant (p < 0.01) reduction in the mean number of hot flushes per week was observed in participants who were receiving the standardized soy extract, whereas a more marked relief was observed in both soy and placebo groups during CEE administration. Concurrently, the severity of hot flushes, assessed by means of the Greene climacteric scale, was also reduced in the soy group participants (p < 0.001, by paired t-test). No soy-related changes were observed on vaginal cytology, endometrial thickness, uterine artery pulsatility index, or metabolic and hormonal parameters tested. Finally, CEE-related changes on genital tract, uterine vascular compartment, and pituitary hormones were not modified by soy treatment. SOYSELECT may be a safe and efficacious therapy for relief of hot flushes in women who refuse or have contraindications for hormone replacement therapy.