We have previously reported on peripheral blood lymphocyte (PBL) transformation by allergen, PPD as a control antigen and PHA as a mitogen during and after a preseasonal immunotherapy period. The present report describes similar parameters during and after the ensuing maintenance treatment period. Ten patients with grass pollen rhinitis were treated with Allpyral extract and 10 with Conjuvac two-grass mixture. Lymphocyte transformation responses to grass antigen continued to be low for PBL from patients during the maintenance treatment. Postseasonal values were higher during treatment. In late autumn 1980, when treatment had been stopped, there was a spontaneous fall in lymphocyte stimulation values. Occasional high values were noticed in some patients, two of whom had treatment side effects (urticaria). Clinical data during the whole treatment period (skin prick test, provocation tests, serological parameters, total IgE, grass-specific IgE, grass-specific IgG, pollen counts, symptom scores, clinical effect and adverse reactions) have been published separately.