A whole body counting technique using ultralow doses of 59Fe and 65Zn in absorption and retention studies in humans.

A whole body counting technique is described which allows monitoring of gamma ray emission rates from body levels of 59Fe and 65Zn in the same range as emission rates of gamma rays from naturally occurring 40K in the total body. Consequently absorption/retention studies were performed with doses of 0.1 microCi. Experimental results from studies using corn intrinsically labeled with 65Zn and wheat intrinsically labeled with 59Fe are presented and illustrate how absorption of 59Fe as low as 4% and retention of 65Zn up to 418 days were measured in humans.