Summary 1. Direct smear of nasal mucus has revealed gram-negative bacilli in 80 per cent of patients with known whooping cough as compared to 12 per cent in cases not suffering from whooping cough. 2. Cough plate cultures (taken in triplicate) were positive for Hemophilus pertussis in 55 per cent of instances compared to cultures of nasal mucus which were positive in 42 per cent of the cases. 3. Both culture methods used simultaneously were found to be superior in isolating Hemophilus pertussis to either one alone. In conclusion, it is felt that direct smears of nasal mucus in the early stage of whooping cough are helpful but not infallible in obtaining preliminary evidence in the diagnosis of the disease. With our technique cough plate cultures (taken in triplicate) are superior to nasal mucus cultures in isolating Hemophilus pertussis from patients with whooping cough at any age up to 14 years.