In the present work two commercially available immunoassays for allergen-specific IgG4 detection were compared, IgG4 FAST Test and ALLERBLOCK-MS IgG4 EIA Kit. For this purpose 30 serum samples were tested for IgG4 antibodies (Abs) specific to Dermatophagoides pteronyssinus (Dp) by the two immunoassays. Eleven serum samples were collected from normal subjects, 6 from Dp-atopic patients never treated by specific immunotherapy (ITS) and 13 from Dp-atopic patients previously treated by ITS. Pearson's linear correlation analysis showed a significant correlation of results from the two immunoassays. However, a better discrimination of Dp-specific IgG4 values between ITS-treated and untreated patients or normal subjects was obtained by FAST than ALLERBLOCK-MS method; moreover, the former showed a better intra-assay coefficient of variation than the latter.