The Clinitemp Fever Detector (a registered trademark for the Clinitemp Co, Indianapolis) is a plastic strip thermometer designed to be placed on the forehead and to detect body temperature by changing color. In a sample of 613 patients, we evaluated the ability of the Clinitemp to detect fevers detected by traditional mercury/glass thermometers. When a Clinitemp reading of 37.8 degrees C (100 degrees F) was used to demark fever, the Clinitemp detected 34% of the clinically significant fevers detected by the mercury/glass thermometers. The sensitivity of the Clinitemp rose to .81 when a Clinitemp reading of 37.2 degrees C (99 degrees F) was used to demark fever. The accuracy of the Clinitemp was affected by variations in ambient air temperature. A reassessment of previously published evaluations of plastic strip thermometers suggest that our results are consistent with other experimental findings. We conclude that the Clinitemp is unacceptable as a substitute for the mercury/glass thermometer.