The relative contribution of uterine activity obtained by home monitoring with a guard ring tocodynamometer compared with seven specific signs and symptoms reported during patient/nurse contact as an aid in detecting preterm labor has not been studied. In this prospective, multicenter study, patients at risk for developing early labor who were randomized to receive home uterine activity monitoring and perinatal nursing support were assessed. The initiator of provider contact (uterine activity detected on routine transmission, patient-perceived signs and symptoms of preterm labor during perinatal nurse contact, or both) resulting in a diagnosis of preterm labor was recorded. Contraction data were then analyzed for an association with preterm labor. There was a strong association of increased uterine activity (four or more contractions per hour) on a repeat monitoring strip with preterm labor (P less than .001). Among patients diagnosed with preterm labor, 31% had increased uterine activity detected on a routine transmission without patient-reported signs and symptoms, compared with 24% who were diagnosed as the result of patient-reported symptoms without increased uterine activity. Daily objective uterine activity data alone have greater incremental value over and above other signs and symptoms as an aid to the physician in diagnosing preterm labor.