In order to standardize and harmonize testosterone measurement, it is vital to identify and minimize pre-analytical error as well as standardize them when developing reference intervals. These pre-analytic issues can be separated into technical and biological factors. Technical factors to address are the type of sample (serum vs. plasma), the type of collection tube, and the processing, storage, and handling of the samples. Biological issues include addressing the age of the subject, the time of day and month the sample is drawn, and all of the possible interfering drugs the subject may be taking. We recommend that great attention be paid to these pre-analytical issues before the assay methodologies are harmonized.