5,340 young adult males, including 5,149 healthy persons, 141 N. meningitidis carriers, 25 patients with generalized meningococcal infection and 6 patients with nasopharyngitis of meningococcal etiology, were examined. The study revealed that red blood cells of 17.4% of healthy persons were highly sensitive to N.meningitidis adhesion (adhesion indices equal to 0.25 and less), red blood cells of 20.4% of persons had low sensitivity to N.meningitidis adhesion (adhesion indices equal to 2 and greater). All other persons with high sensitivity of their red blood cells proved to be patients with meningococcal infection or carriers of N.meningitidis of the same group.