In the questionnaire survey of Phase I, 249 out of 3436 (7.3%) students reported 6-10 common colds in the previous 12 months, while 94 (2.8%) reported more than 10 common colds. Four hundred and thirty six (12.8%) students had common colds lasting for 2-4 weeks, while 65 (1.9%) reported colds lasting more than 4 weeks. Demographic information and living habits of dormitory occupants, and their associations with common cold are summarized in Table 1 . Atopy was associated with increased incidence and longer duration of common cold. Male students were more susceptible than females, but had shorter duration colds. Females cleaned rooms more often than males, cleaning rooms at least twice per week 52% compared to 31% for males, and smoked less (1.4% vs. 15.9%). Passive smoking had a significant effect on the incidence of common cold (p = 0.029), but after adjustment for environmental tobacco smoke, males were still at greater risk for common colds (p = 0.010). Younger students lived in more crowded rooms and reported longer duration colds. Crowding, not age, was shown by stratification for occupancy level to be the significant association with common cold duration.