Human immunodeficiency virus (HIV) has been isolated from both male and female genital secretions. We evaluated the pattern of female genital carriage during the menstrual cycle, and its relationship to HIV viremia. Seven menstruating seropositive women and one seronegative control had cervical secretions and venous blood samples cultured at weekly intervals during a single menstrual cycle. The virus was isolated from cervical secretions in four of seven women. No specific cycle pattern was seen, and positivity for HIV at one site (blood or cervical) did not correlate with positivity at another site. Blood cultures generally, but not always, became positive earlier than cultures from cervical specimens, suggesting higher titers of virus in blood. Thus, HIV secretion may be intermittent. These findings, together with earlier reports, suggest that seropositive women may transmit HIV at any time during the menstrual cycle.