The Vitamin A and Zinc: Prevention of Pneumonia (VAZPOP) study was a multi-year nutritionally-stratified, placebo-controlled, double-blind study of low-dose vitamin A and/or zinc in 2,582 normal and malnourished urban children aged 6 to 36 months in Quito, Ecuador. Four group of ~ 645 children were enrolled in 2000, 2001, 2002, and 2003 with each child participating for up to 50 weeks. Children were visited 4 days each week. Outcome measures were pneumonia, other respiratory tract infections, diarrheal disease, and growth.