Bioavailable Testosterone (BT) is henceforth well-known to be much more useful than Total Testosterone (TT) for interpretation. BT is mostly explored in case of suspicion of hypogonadism in men or hyperandrogenism in women. The reference technique to assay BT is ultracentrifugation, but Radio-Immuno Assay (RIA), which is much less expensive and easier to accomplish is the most widely used technique in practice. Several calculations are available but the one that give the better results seem to be the optimized calculation of the Vermeulen equation by Giton. Very few comparisons between BT assayed and BT calculated have been made in routine, hence our study. This is a prospective study which has included 269 patients (whose 189 men) to compare both results in the frame of matched data. Different subgroups, depending on gender, age, TT values, SHBG values and albumin values have been studied. Although BT calculated values seem to be significantly higher to those in RIA, correlation appear to be excellent in men with a correlation coefficient established at 0.92, but not in women. BT calculated appear therefore to be an excellent alternative to assay, and has obvious other advantages: It is free, allow faster result delivery and a blood test requiring one tube less for patients.