Physiological cervicovaginal acidity can partly inactivate human immunodeficiency virus (HIV). Basic semen components should be able to partially neutralize in vivo cervicovaginal pH. The goals of the study were to evaluate the relationship between cervicovaginal pH and presence of semen components in sexually active African women and to assess whether vaginal douching with water performed just after sexual intercourse could significantly reduce semen components and restore physiological cervicovaginal pH. Cervicovaginal secretion (CVS) from 56 heterosexual African women (19 to 45 years old), living in Bangui, Central African Republic, were evaluated for pH, semen components (prostatic acid phosphatase [PAP] and prostatic specific antigen [PSA]), cellularity, and hemoglobin at inclusion and after vaginal douching with 100 ml of water by using a bock. Before douching, semen components were found in 46 of 56 CVS (82%). The mean vaginal pH was 5.2 (range, 3.6 to 7.7), and concentrations of both PAP and PSA correlated positively and strongly with cervicovaginal pH (P < 0.001). After douching, semen components were found in 35 of 56 CVS (62%) (P = 0.03). Cervicovaginal PAP and PSA levels were significantly decreased (respectively, P < 0.0001 and P < 0.01; PAP, -72%; PSA, -87%), as was the total cell count (-60%; P < 0.0001). Furthermore, in CVS previously positive for both PAP and PSA, the mean vaginal pH was significantly decreased (6.5 versus 5.3, P < 0.01); no genital bleeding was observed. Frequent persistence of semen in CVS from heterosexually active African women leads to a shift from acidity to neutrality that could favor male to female HIV transmission. Vaginal douching provides significant elimination of semen after sexual intercourse; it should be considered for study as a supplementary means for the prevention of heterosexual HIV transmission.