During 1971-77 the incidence of bacterial meningitis among Alaskan Eskimos was 84.4 cases per 100 000 population per year, which is more than 10 times that for most other U.S. populations. Haemophilus influenzae (HI) accounted for 68% of meningitis cases. The average annual incidence of HI disease per 100 000 children below 5 years of age was 409 for patients with meningitis only and 491 for patients with all systemic HI disease. Children with HI meningitis in Alaska tended to be younger than those in other U.S. populations, 98% of the children affected being less than 18 months of age. The risk for all HI disease was 2.4% during the first year of life. The spectrum of HI disease in Alaska differs from that in other populations in that no patient had epiglottitis and 5% of children had recurrent HI disease. Alaskan newborns and children over 4 years old had HI anticapsular antibody titres that were nearly thrice those for children of similar ages in other U.S. populations (p<0.005). The pharyngeal carriage of HI type b (5%) and the rectal carriage of Escherichia coliK100 (2%), an organism with a capsule antigenically similar to HI type b, did not differ from those in other populations. The high incidence of disease almost exclusively in the very young and the early development of antibody in this population suggest that the high rate of disease is due to early exposure to HI type b rather than to an unusual susceptibility to HI type b.