The present work reports the results of a double-blind clinical trial, comparing the effects of hyposensitization treatment versus placebo in 33 patients with allergic rhinitis, sensitive to a crude extract of the pollen of four different grasses (Dactylis glamerata, Lolium perenne, Secale cereale, and Phlewn pratense). The distribution of these patients in the two groups was done randomly and gave two comparable groups, as far as clinical and biological features are concerned. The treatment course included five low doses of the aqueous extract followed by 12 injections of Al(OH)3-adsorbed aliquots of the same extract. Evaluation of the clinical scores was based on diary cards on which symptoms and medications were recorded. A reevaluation of the significance of the symptom and medication scores is presented and the link between both scores is studied. Particular attention is given to the methodological and statistical problems raised during this study. The non-parametric tests reveal a significant difference (P < 0.03) in the total clinical score between the treated and the placebo groups for the second half of the observation period, when the pathology was most intense.