Abstract 1. 1. Among 143 allergic subjects between the ages of 18 and 35 years who were challenged with infectious secretions taken from patients with a common cold, 45 per cent developed colds, as compared with 31 per cent among 693 nonallergic subjects who were challenged in the same way. These differences were statistically significant. 2. 2. Among 363 subjects whose tonsils had previously been removed, colds followed experimental challenge in 34 per cent, as compared with 32 per cent colds among 464 subjects whose tonsils were intact. 3. 3. Among 249 persons who smoked tobacco, 35 per cent developed colds following experimental challenge, as compared with 34 per cent among nonsmokers. 4. 4. Among 13 female volunteers who were chilled and given an infectious secretion during the middle third of the menstrual cycle, 10 (77 per cent) developed colds as compared with 28 and 30 per cent of subjects similarly treated who were challenged during the first or the last third of the menstrual cycle, respectively. The differences between the incidence of colds in chilled subjects challenged during the middle third and those chilled and challenged during the first or last thirds of the menstrual cycle or those challenged during the middle third of the menstrual cycle without being chilled, were statistically significant.