Preseasonal local nasal immunotherapy (LNIT) by means of an extract in macronized powder form has been studied in allergic rhinitis to parietaria. Twenty-four Parietaria-sensitive patients have been studied for 18 weeks in a double-blind controlled trial. Subjects were selected on the basis of a positive skin test, RAST and intranasal challenge to Parietaria antigen. Three eight-patient groups were randomly planned: the first group was given native Parietaria product, the second modified Parietaria product, and the third placebo. During the pollen season no difference was observed in mean weekly symptom score between the three groups, while the mean weekly medication score was significantly lower in the treated groups than the control group. Only the treated groups showed a significant increase in specific nasal threshold to Parietaria after treatment. Adverse reactions to LNIT, limited to the upper respiratory tract, occurred rarely and did not interfere with the dose schedule. This study indicates that LNIT in powder form may be a suitable alternative to the traditional subcutaneous immunotherapy in terms of clinical efficacy and safety.