PIP: An accurate record of oral basal temperatures, taken every morning b efore beginning any activity, can provide pertinent data on ovarian acti vity and ovulation. Oral temperatures are just as reliable as rectal or ovarian temperatures and are more acceptable to the patient. Basal temperature graphs collected from 500 patients over a 2-year period show a definite temperature drop followed by a pronounced rise at time of ovulation; in many cases vaginal smears, endometrial biopsies, and operative material confirmed this phenomena. The higher level continues through the later half of the cycle, dropping sharply just before menstruation. When pregnancy occurs the basal temperature remains at the postovulatory level through the 1st few months of gestation. It then drops but does not return to the preovulatory level until after delivery. Postpartum basal temperature curves indicate that the 1st bleeding period is rarely ovulatory while the 2nd menstrual period is associated with ovulation in about 1/2 the patients. A basal temperature curve should be part of every sterility study; it is the simplest device for ascertaining ovarian activity and dating ovulation. In 75% of sterility cases determining time of ovulation has resulted in conception. Basal body temperatures which continue elevated provide the most accurate early data concerning pregnancy. During the 1st week of a missed menstrual period the failure of the temperature to drop strongly indicates possible pregnancy. Patients with characteristically irregular periods will not yield as much information through temperature curves. Basal temperatures are reliable indexes of ovarian activity in at least 3 out of 4 women. In the 4th the curve is so atypical with irregular readings at intervals that no accurate interpretation of physiological changes can be made. In addition to fertility studies and indications of pregnancy, basal temperatures can aid in conception control by pinpointing time of ovulation. The woman is to refrain from intercourse from the preovulatory drop until 36-48 hours after the ovulatory rise has reached a plateau. This system has also helped women avoid conception in the menopausal period. 1 group followed their basal temperatures during the climacteric. Fewer and fewer periods were associated with ovulation and when bleeding ceases entirely the curve assumes the typical diurnal pattern seen in the male for ovarian activity is at a low ebb.