AbstractDeuterium labeled forms of 5α‐androst‐16‐en‐3‐one, 3α‐hydroxy‐5α‐androst‐16‐ene, 3β‐hydroxy‐5α‐androst‐16‐ene, 3β‐hydroxy‐5, 16‐androstadiene and 4, 16‐androstadien‐3‐one were prepared to serve as internal standards in quantitative analysis of C19‐Δ16steroids by mass spectrometric reverse isotope dilution. In general, the methods used employed deuterium exchange of activated hydrogens adjacent to carbonyl carbons followed by reaction steps which isolated the newly incorporated deuterium. Removal of any remaining exchangeable deute