--Population Characteristics-- Newborns enrolled at first vaccine clinic visit Weight at first vaccination at least third percentile, i.e.: Girls: 3.2 to 3.8 kg Boys: 3.4 to 4.0 kg No previous illness compatible with pertussis --Prior/Concurrent Therapy-- No prior pertussis vaccination --Patient Characteristics-- Age: Over 6 weeks to under 12 weeks Renal: No renal failure Other: No prior prolonged immunosuppressive therapy No prior systemic corticosteroids, unless duration less than 14 days and at least 48 hours since last dose No major congenital abnormality No failure to thrive No known or possible immune system deficit, e.g.: HIV-infected mother Autoimmune anemia Lymphoma Other erythropoietic disease No perinatal central nervous system disease or damage No history of convulsions Mother Italian-speaking and accessible by telephone Planned residence in clinic district for at least 1 year