A method of estimating the peripheral plasma concentration of 11-deoxycorticosterone (DOC) in man by means of gas-liquid chromatography with electron capture detection is described. Purification requirements for samples and chromatographic media have been simplified by the use of a detector bypass valve which reduces the risk of detector contamination. For this reason the method is relatively short. There was no measurable blank using either plasma from an adrenalectomized subject or water. The normal range was found to lie between 4·1 and 17·2 ng/100 ml (mean 9·8). Dexamethasone administration to one subject resulted in a subnormal plasma DOC concentration.