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THE nasopharyngeal swab, which has been used in the past in the diagnosis of pneumonia and in the detection of meningococcus carriers, was adapted by Bradford, Slavin, and Brooks1, 2 to the diagnosis of whooping cough. The value of this method has been confirmed by Anderson3 and in a preliminary study by the present authors.4 Recently Brooks, Bradford, and Berry5 have reported their findings in a total of 438 nasopharyngeal cultures from 248 cases of pertussis. A somewhat smaller number of cough plate cultures were taken for comparison. Fifty-two per cent of the nasopharyngeal cultures were positive as compared to 37 per cent of the cough plate cultures. In infants under 3 years of age the difference in the results with the two procedures was most marked -32 per cent.The following report amplifies our previous one and contains some data on the carriage of Hemophilus pertussis by familial contacts.The nasopharyngeal applicator and the technic of insertion have been fully described.1 4 The Bordet-Gengou medium we employed was the same as previously reported 4 and differed from that of the Rochester workers in that 33 per cent horse blood was added instead of 15 per cent sheep blood. Fresh media were prepared every 2 weeks. It did not appear necessary to pour plates any more often. For both the cough plate and swab cultures, Petri dishes 3Y2 inches in diameter were used.At least two Petri dishes of medium were inoculated with each swab, and the cough plates were also usually taken in duplicate.The cultures were obtained by many different physicians and nurses. In more experienced hands better results might be expected.One or more duplicate tests with nasopharyngeal swabs and cough plates were made in 214 cases of whooping cough. A total of 342 comparative cultures were examined. The results are classified according to the duration of the disease in Table 1.During the first week 74 cultures were taken. In 32 both plate and swab were positive, in 6 the plate only was positive, in 22 the swab only was positive, and in 14 both cultures were negative. Eighty-one per cent were thus positive by both or either means. It is therefore apparent that the cultural methods available for the diagnosis of pertussis in the catarrhal stage are relatively [839]