In a prospective, double-blind, placebo-controlled study of iv immunoglobulin (IVIG) and trimethoprim-sulfamethoxazole (TMS), 130 children less than 8 years of age were referred for recurrent bacterial respiratory tract infections, as judged by the referring physician. Of the 130 children referred, only 24 continued to have bacterial respiratory infections over a 4-month observation period. They were randomized and 23/24 treated for 4 months during the winter-spring season. The 7 children given placebo for both IVG adn TMS continued to have bacterial respiratory infections, while 14 of 16 children given active therapy with either IVIG or TMS became infection-free (p=0.002). No relation to IgG subclass level or between the two modalities of treatment was found. We concluded that most infection-prone children suffer from viral infections and are given antibiotics unnecessarily. Of the small group of children that have documented, repeated bacterial infections, prophylactic therapy with either IVIG or TMS can substantially diminish the number of infections.