The authors describe a detector column which consists of high-specific activity 64Cu complexed with alkaline Sephadex. The protein solution to be measured is alkalinized with NaOH and pumped at constant rate through the detector column. Radioactivity in quantities equivalent to the amount of protein added is eluted and measured with a ratemeter furnished with a recorder. The method permits determination of protein in submicrogram quantities. It is insensitive to ammonia and various other small-molecular substances forming complexes with copper. A preliminary study was made on the elution properties of amino acids, peptides and various other substances and a rough estimate of the stability of the copper-Sephadex complex was obtained. In model runs, DEAE-cellulose chromatography patterns were produced for tear fluid and endolymph.