Doctor's pens and pen sets come in many variants, the common denominator being an incorporated thermometer. The earliest doctor's pens, such as the celebrated models offered by Parker and OMAS, were eyedroppers with internal compartments for the thermometer, which was withdrawn from the end of the barrel opposite the nib. An example of the type by Laughlin appears below.

More commonly, doctor's sets paired a standard fountain pen with a matching thermometer case; a pencil was often part of the ensemble.  The Waterman 52 set below is an early example.

After the advent of celluloid, these sets were often made in white, though not always. The 1930s Vacumatic doctor's set below used the standard silver pearl laminate.

Doctor's pens are quite scarce, and those in light colors are usually found with discoloration and cracks. Nurse's pens and sets, however, which use smaller pens and usually lack the thermometer, are considerably more common; most often seen are the 1940s Watermans in ivory pearl with either red or black cap crowns, and the 1950s Esterbrook purse pens in white.