To the Editor: The article by Holmberg et al. in the September 6 issue1 has serious deficiencies that invalidate the authors' claim to have demonstrated a link between the subtherapeutic use of chlortetracycline in cattle feed and an outbreak of Salmonella newport food poisoning in patients undergoing antibiotic therapy. No evidence is presented that S. newport was ever present on the beef farm alleged to be the source of the infection. Nor do the authors report whether they attempted to isolate salmonella from human beings, animals, or meat products from the beef farm. The only occurrence in animals of S.