Specific antibodies to ragweed pollen antigens were studied in 22 patients given preseason Pollinex-R (glutaraldehyde-modified ragweed tyrosine-adsorbate) (PR), 17 without immunotherapy, and 8 on maintenance doses of aqueous ragweed extracts. The PR-group showed about fourfold increases in IgG antibodies in season when compared with pretreatment levels (P less than .001). IgG antibody changes from before season to season in other groups and IgE antibody changes in all three groups were not significant. Despite this, IgG antibodies in season had fallen from their peak achieved with PR. About one-third of PR-treated patients still manifested significant symptomatology irrespective of changes in IgG antibodies. We thus conclude that although changes in specific IgG may be an important correlate in PR-immunotherapy, additional mechanisms for clinical responsiveness remain to be clarified.