Abstract
This study is based on the records of sickness absence of four days or longer attributed to bronchitis among nearly 60,000 London Transport employees during the years 1952 to 1956. The figures support previous observations that there is a close association between the incidence of bronchitis and the occurrence of fog in any year. The bronchitis experience of employees living and working in the north-eastern sector of London is shown to be worse than in other areas of London. The experience of employees in the country belt round London, particularly in the southern sector, is better than in London itself. With the possible exception of conductors, the figures do not suggest that there are occupational factors in the transport industry causing bronchitis.