van de Velde's observation as to the existence of variations in body temperature during phases of the menstrual cycle was cited in a previous editorial.1 Rubenstein2 correlated a study of vaginal smears with a study of basal temperature; he found that the basal rectal temperature tends to drop progressively during the phase of follicle development. The low point in the temperature curve is reached when the follicle matures. Barton and Wiesner3 found in their studies of the temperature in several hundred women that the body temperature on waking in the morning varies in fecund women with the phases of the menstrual cycle. A relatively high temperature is characteristic of the premenstrual phase, and it persists after conception. Persistent low temperature excludes the diagnosis of pregnancy. The diphasic temperature cycle may persist in cases of amenorrhea, but more commonly amenorrhea is characterized by a monophasic waking temperature record.