A new rapid electronic thermometer (V.C.T. TERUMO) has been introduced to Danish hospitals. Oral and rectal V.C.T. measurements were compared with rectal measurements with mercury thermometers. In addition, rectal V.C.T. measurements in the wards were compared with rectal measurements with mercury thermometers. A total of 91 patients participated in the investigation. The average differences between the electronic rectal and oral compared with recordings by mercury thermometers were found to be 0.02 degree C and 0.75 degree C, respectively, under optimal conditions for measurement while the corresponding scatters of difference in temperature were 0.17 degree C and 0.74 degree C, respectively. The average difference between rectal temperature measurements with mercury thermometers and rectal V.C.T. measurements carried out during daily routine circumstances was 0.08 degree C while the scatter of the difference in temperature was 0.26 degree C. It is concluded that rectal V.C.T. measurements are just as suitable as rectal measurements with mercury thermometers and employment of rectal V.C.T. thermometer measurements is recommended in the daily hospital routine. Employment of oral and axillary measurements is discussed and not recommended.