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In connection with a report in 1934 on the results of cough plate examinations for Bacillus pertussis (Kendrick and Eldering, 1934a) we noted that all of 136 strains isolated from patients with whooping cough were similar serologically and corresponded with Leslie and Gardner's Phase I (1931). Since then, up to June 1st, 1937, the total number of Phase I cultures has increased to 1498. During that period we have isolated from seven whooping cough patients ten cultures which resemble B. pertussis in certain respects but do not conform with all the criteria ascribed to Phase I. Strains similar to these ten were not recovered from over 1500 cough plates from patients with upper respiratory infections other, than whooping cough. On the original cough plates from which these organisms were recovered the colonies were typical of B. pertussis after 48 hours incubation. Morphology and staining reaction appeared typical of B. pertussis and agglutination tests were positive with B. pertussis antiserum in low dilution. The plates were reported positive for B. pertussis to the attending physicians. However, after longer incubation the colonies on these cough plates were observed to be unusually large and, unlike B. pertussis, were found to grow profusely on plain infusion agar and in broth. Recognizing a possible relationship to Bacillus bronchisepticus, we tested the cultures 1 The authors gratefully acknowledge the technical assistance of Gertrude Hodges. For financial assistance, they are indebted to the National Research Council.