A method is proposed for the solvent extraction of cobalt using 1,5-bis(di-2-pyridylmethylene) thiocarbonohydrazide (DPTH) as extractant. The optimum extraction conditions were evaluated from a critical study of the effect of pH. concentration of extractant, shaking time and ionic strength. The maximum volume ratio of the aqueous to organic phase was 30:1 for a single-stage extraction of 99-100 % of the metal ion. The detection limit is 0.9 ng/ml cobalt, and the calibration is linear from 0.9 to 1000 ng/ml. The effect of interferences was studied and no interferences from the elements commonly found in biological materials were observed. The extraction method was applied to the determination of cobalt in some biological materials using inductively coupled plasma atomic emission spectrometry (ICP-AES).