The development by Alexander1of a therapeutic type-specific rabbit serum has dramatically influenced the prognosis in infections by Haemophilus influenzae, type b. In our own series of cases of meningitis by this organism, the mortality was 100 per cent (11 out of 11 cases) prior to the use of rabbit serum, and 15 per cent (4 out of 26 cases) with its use in conjunction with sulfonamide compounds. In the past we have administered the serum intravenously or both intravenously and intrathecally as recommended by Alexander.2Recently 3 babies with meningitis due to H. influenzae, type b, were admitted to the pediatric isolation wards of the New Haven Hospital and afforded an opportunity for the determination of the effectiveness of the serum when administered intramuscularly. REPORT OF CASES Case 1.— G. K., a boy aged 18 months, was admitted with a history of a "cold" with nasal discharge