A new procedure for derivatizing ketosteroids with dansyl hydrazine, a fluorogenic tagging agent, is reported. Termed “evaporative-derivatization”, this technique employs simultaneous heating and evaporation for the derivatization step. Presumably, as the evaporation approaches completion, the analyte is exposed to an infinite concentration of dansyl reagent. The impact of this work provides for a short reaction time (10min), low temperature (60°C), and almost complete derivatization. The short derivatization time enables labile steroids to be tragged with little decomposition. While the prior dansylation techniques tag only the 3-position, this new procedure also tags the sterically hindered 20-position forming a bis-dansyl derivative. The bis-derivative exhibits significantly greater chromatographic retention, which means that chromatographic interferences are less likely when complex matrices, such as extracts of blood plasma are analyzed.