Aqueous iodine (2%) applied to the fingers was effective in blocking had transmission of experimental rhinovirus infection. None of eight volunteers became infected when exposed to rhinovirus immediately after treatment of the fingers with iodine. All of seven similarly exposed subjects treated with a placebo preparation became infected (P less than 0.001, Fisher's exact test). One of 10 volunteers became infected when exposed 2 hr after treatment of fingers with iodine, compared with six of 10 who became infected in the control group (P = 0.06, Fisher's exact test). Virus was recovered from three (11%) of 27 hand rinses from volunteers using iodine and from 11 (41%) of 27 hand rinses from volunteers using the placebo preparation (P less than 0.03), Fisher's exact test).