A rapid one-step method for the separation of granulocytes, mononuclear cells and erythrocytes from peripheral blood using two different gradients of Percoll (density solution I: 1.075 kg/l; solution II: 1.096-1.098 kg/l) is described. The influence of temperature on the density of solution II was tested and the variations were found to be of some importance. The average yield of granulocytes from 14 donors was 87.6 +/- 9.6%, and the purity of the granulocytes was 99.66 +/- 0.33%.