Thirty paired samples of plasma and whole hemolyzed blood were obtained from patients undergoing surgery. Morphine concentrations were measured with the DPC serum morphine kit without prior treatment. In a regression analysis, the equation to the regression line was blood = 1.02 plasma + 1.0 ng/mL, and the correlation coefficient was 0.994. Radioimmunoassay screening of postmortem blood samples can be performed without prior sample treatment.