Liquid-gel chromatography on a hydrophobic hydroxy-alkoxypropyl Sephadex derivative has been used to separate 17α-hydroxyprogesterone from potentially interfering steroids prior to analysis by a competitive protein binding method. The separation is achieved in 5–6 h on a 2 g column using light petroleum/2-methyl-2-propanol, 9:1, as the solvent. The columns can be used repeatedly for long periods of time and one technician can handle 15 columns simultaneously. Mean recoveries of 17α-hydroxyprogesteron added to plasma were 90–95 per cent. The effluent from the columns was free from material interfering in the protein binding analysis.