Sera from 85 consecutive systemic meningococcal disease patients and 203 matched control individuals were C8 typed. In the patient group, one C8B deficient individual was discovered; none in the control group. No case of C8A deficiency was encountered. The material was collected during a period of epidemic meningococcal disease in Norway, mainly due to group B organisms. C8A and C8B phenotype distributions were not significantly different in the two groups. This indicates that no particular C8 type (apart from deficiency) predisposes for meningococcal disease. Neither is there any evidence of over-representation of heterozygous deficiency among meningitis patients. The C8B deficient individual and his family were studied. Tests for haemolytic complement were normal in all members except for the proband. Electrophoretic C8 patterns seemed to be slightly weaker in the heterozygously C8B deficient individuals than in persons with 2 normal C8B genes. DNA from the family members were studied with regard to a restriction fragment length polymorphism (RFLP) for the C8B gene. All exhibited the same pattern, indicating that the C8B deficiency is not due to a major deletion in the C8B gene.