This report describes a radioimmunoassay method for the measurement of unconjugated 11-desoxycarticosterone (DOC) in plasma. Utilizing an anti-DOC antiserum cross reacting minimally with the steroids tested, combined with a one step celite microcolumn chromatography, we have measured this steroid accurately in aliquots of plasma from premenopausal female subjects. The plasma levels of DOC obtained by this method agreed well with levels observed in adult women, using other technics. During the 4 menstrual cycles studied, DOC levels were significantly higher in the luteal phases compared to the follicular phases in all 4 subjects.