Four sample pretreatment methods, three protein precipitation methods, and one sonication/dilution method, were tested. The sonication/dilution method produced the best results. The blood sample was applied onto the column at pH 3.3 after sonication and dilution with 0.1 M phosphate buffer (pH 3.3). Morphine retention was affected by the pH of the samples; the loss of morphine during sample application was minimized at pH 3.3. Interferences were removed by washing the column with the phosphate buffer, 0.01 M acetic acid, and methanol. Ammoniated methanol was used to elute morphine, with the result that more than 80 percent of 3H-morphine was recovered for concentrations of morphine ranging from 5 to 4000 ng/mL. 1 table, 5 figures, and 14 references