A method for determination of zinc contents in very small samples of hair was developed in order to estimate the zinc concentration in the human body. All steps from weighing of samples to ashing and preparation of the test solution were done in a tube designed by us to prevent contamination and to improve handling. Zinc concentration was determined with flame atomic absorption spectrophotometry aspirating a small volume of samples (80 microliters), by the so-called "one-drop method". Using this method, 5 mg of whiskers was analyzed every day for 10 days, and this revealed that the fluctuation of the zinc concentration level was very small and that it was possible to trace the individual level of zinc concentration daily. A sample of 5 mg is enough for the application of this method. Zinc concentration in the hair under the temple of a boy, and even the low-level zinc content of patients receiving total parenteral nutrition could be accurately determined every 10 days and monthly, respectively. The level of hair zinc contents for neonates was similar to that of adults.