Little knowledge is available on molds either from the environmental or clinical points of view. The latter is mainly due to the lack, until recent times, of purified and standardized extracts. Injective immunotherapy, largely used for patients allergic to mites and pollens, is regarded with some concern for molds. On the other hand, mold-related allergic symptoms (i.e.,from Alternaria tenuis) have in Italy an incidence of about 5 percent, mainly in young patients. We have therefore run a pilot study comparing the efficacy and safety of injective (SIT) and sublingual (SLIT) immunotherapy by administering the same purified and standardized extract of Alternaria tenuis to a total of 23 patients for two years, according to an open experimental plan. Excellent tolerance was shown to SLIT while four (two medium-grade) side effects appeared with SIT. Clinical improvement, subjectively stated comparing symptoms (mainly rhinitis) and drug consumption before and after the therapy, confirmed by an increase in the Specific Nasal Provocation threshold, was obtained with both therapies, but with a statistically significant difference in favour of SLIT. Skin reactivity and blood Alternaria tenuis specific IgE, total IgG and IgG changed in the SIT-treated group, while no statistically significant change was shown in the SLIT-treated group. These results are in good agreement with previous reports on SIT and SLIT with other inhalant allergens (mites, grasses), and suggest the potential use of SLIT for Alternaria allergy, mainly in young patients, when there are concerns about the safety of and compliance with the traditional injective therapy.