Rat lymphocytes can cause destruction of sheep's erythrocytes (SRBC) in Hanks solution (containing Ca~(++) and Mg~(++)) at 37℃. The breaking down of SRBC releases hemoglobin. The quantity of hemoglobin can be measured by 721-spectrophotometer. It is suggested that the lymphocytes which made lysis of SRBC might be the natural killer cells.

Human peripheral blood lymphocytes and sheep red blood cells(SRBC)were incubated together in Hanks solution containing Ca~(2+) and Mg~(2+) ion, causing SRBC destruction and release of hemoglobin, 500%hemolysis value was found to 6.1921?0.06. The destruction of SRBC by lymphocytes was inhibited by trypsinase, its 50% hemolysis value became 0.0348?0.03 (P