A column liquid chromatographic method for the simultaneous determination of chloroquine, amodiaquine and their monodesethyl metabolite in human plasma, red blood cells, whole blood and urine is described. The drugs and internal standard were extracted as bases with methylene dichloride and then re-extracted into an acid aqueous phase. Separation was obtained using a reversed-phase column and a mobile phase of phosphate buffer (pH 3.0)-acetonitrile (88:12). The absorbance of the drugs was monitored at 340 nm with a sensitivity limit of 10 pmol/ml. No endogenous compound interfered at this wavelength. The mean overall recovery from each biological fluid was greater than 75%. This method can be applied to therapeutic, pharmacokinetic and epidemiological studies. The metabolism of these two amino-4-quinolines in humans is compared.