John Kingsbury Frost (c. 1922 - 1990) was an American physician specializing in the field of cytopathology - the microscopic study of individual body cells to detect cancer and other diseases. The first area of the body to be studied in this way was the female genital tract, using the Pap smear invented by Georgios Papanikolaou. Frost and other physicians expanded the field to allow for cytopathologic evaluation of the lung, bladder, and many other body sites. Frost was best known as a teacher of cytopathology. He organized and directed a school of cytotechnology and created and led a postgraduate Institute to teach the techniques to physicians.