In the first of three studies investigating the widely held belief that "milk produces mucus," 60 volunteers were challenged with rhinovirus-2, and daily respiratory symptoms and milk and dairy product intake records were kept over a 10-day period. Nasal secretion weights were obtained by weighing tissues collected and sealed immediately after use. Information was obtained on 51 subjects, yielding 510 person-days of observation. Subjects consumed zero to 11 glasses of milk per day (mean, 2.7; SE, 0.08), and secretion weights ranged from zero to 30.4 g/day (mean, 1.1; SE, 0.1). In response to an initial questionnaire, 27.5% reported the practice of reducing intake of milk or dairy products with a cold or named milk or dairy products as bad for colds. Of the latter group, 80% stated the reason as "producing more mucus/phlegm." Milk and dairy product intake was not associated with an increase in upper or lower respiratory tract symptoms of congestion or nasal secretion weight. A trend was observed for cough, when present, to be loose with increasing milk and dairy product intake; however, this effect was not statistically significant at the 5% level. Those who believe "milk makes mucus" or reduce milk intake with colds reported significantly more cough and congestion symptoms, but they did not produce higher levels of nasal secretions. We conclude that no statistically significant overall association can be detected between milk and dairy product intake and symptoms of mucus production in healthy adults, either asymptomatic or symptomatic, with rhinovirus infection.