A primarily clinical trial has been undertaken to investigate and compare the use of mercury and digital thermometers in a ward situation. Both laboratory and clinical studies show that there is no significant difference in the average accuracy of the two types of thermometers, however there is a greater fluctuation of readings of temperature when using electronic thermometers. In clinical studies between 9 and 23% of repeated measurements using an electronic thermometer differ by 0.5 degrees C or more whilst the corresponding range for mercury thermometers is 0.6%. It is also shown that when making clinical measurements with mercury thermometers there is no clinical advantage in using a measurement time longer than 3 minutes.