Abstract: A fibrinogen monitor for use in monitoring the concentration of iodinated fibrinogen distribution in the calf and thigh veins of bed-restricted patients. The fibrinogen monitor is an improved scintillation detector which a hospital staff member can manipulate using one hand to detect and record scintillation events at measured points along the leg of a patient while leaving the other hand free to aid in positioning the leg. The output of the monitor is digitized and provided both as a visual display and as a hard-copy record. The geometrical configuration of the probe of the monitor provides for increased sensitivity to gamma radiation without an attendant increase in probe size.