The purpose of this study was to describe core temperatures measured by esophageal temperature and a swallowed, telemetry sensor in women during exercise when wearing clothing with high thermal resistance ( R T, 0.4 m −2 · K −1·W −1). Resting esophageal temperature ( T es) averaged 37.11 ± 0.21°C and resting pill temperature ( T pill) averaged 37.17 ± 0.27°C. The combination of exercise (225 ± 30 W m −2), clothing and ambient temperature ( T a = 30°C) caused T es to increase to an average of 38.67 ± 0.28°C and T pill to increase to an average of 38.71 ± 0.33°C during the hour of treadmill walking. The two temperature measurements were compared by least squares regression techniques. For the eight individual experiments run, the regression coefficient ( r) averaged 0.98 ± 0.01. The calibrated temperature sensor ingested in these experiments provided accurate, usable core temperature data during logistically difficult experimental conditions.