Three controlled trials of attenuated live influenza vaccines in patients with chronic bronchitis with airways obstruction are described. A recombinant virus with parentage from PR8/34 (H1N1) and A/Alaska/77 (H3N2) was present in the vaccine (RIT 4199) used in the first two trials. In the third trial a cold-adapted recombinant virus vaccine (A/Washington/80, H3N2) was used. No adverse effects were noted in the first two trials in which half of the patients responded serologically to the vaccine. In the third trial increases in upper respiratory symptoms occurred in the first week after vaccine was inoculated. One patient, who did not respond serologically to the vaccine, developed a temporary sharp decline in FEV1.0 and FVC. We have no explanation other than the preinoculation HI serum antibodies for the low rate of serological response (9 of 29) in the vaccinated patients in the third trial.