Aedes albifasciatus (Diptera: Culicidae) is the most common mosquito species in Argentina and it has been demonstrated to be the vector for some pathogens. The objective of this study was to describe the allergen composition of this mosquito species endemic to Argentina using SDS-PAGE and immunoblotting methods. Sera from mosquito-bite allergic subjects were employed. The protein extracts, obtained from thoraxes containing salivary glands, showed a protein pattern with components of apparent molecular weights ranging from 14 to over 94 kDa. Some of the components could bind IgE in the 16, 20, 30, 36 and 50-67 kDa-zones, whereas the 14 kDa fraction detectable by SDS-PAGE did not behave as an allergen with any positive serum. This protein extract was used to develop in vitro assays to detect the presence of serum-specific IgE against proteins from A. albifasciatus (RAST and ELISA). Thirty-five sera from patients showing local reactions after mosquito bites were tested. The 21 positive sera were from subjects with clinical histories of atopic signs. Through immunoblotting, these sera revealed IgE reactivity against several fractions, mainly in the 16, 20, 30, 36 and 50-67 kDa zones. Comparing the serum IgE reactivity pattern against A. albifasciatus and Aedes aegypti, we observed that the main difference was found in the 14 kDa region where a strong reactivity was seen. The immunoblotting inhibition results indicate that there might be species-unique and species-shared antigens between A. albifasciatus and A. aegypti.