To evaluate the in vivo effect of autologous serum including antibodies to house dust mite in atopic individuals, we observed the immediate (15 mins) and late (6 hours) skin reactions (ISR, LSR) on intradermal (ID) test of serially diluted Dermatophagoides farinae antigens (DFa, Allergopharma, Germany) mixed with autologous sera (DFa-S) and diluent alone (DFa-D). We tested 34 DFa-skin reactive atopic individuals including 12 asthmatics (BA), 8 asthmatics on immunotherapy with DFa (IT), and 14 healthy atopic controls (AC). We observed complete inhibition of ISR in the lowest allergen dose of DFa-S in 7 (58.3%) of 12 BA, 3 (37.5%) of 8 IT, and 2 (14.3%) of 14 AC. In BA, the inhibition of ISR was more frequent than AC (p < 0.05). We observed larger late reactions in half of LSR positive cases on ID test by DFa-S than by DFa-D (> or = 1.5 X size; accentuation of LSR). Accentuation of LSR were shown more frequently by DFa mixed with larger amount of serum (25% in 1:1 mix; 80% in 1:3 mix, p < 0.05). But there were no differences of DFa-specific IgE and IgG subclass antibodies regardless of the inhibition of ISR or the accentuation of LSR. In conclusion, some autologous sera from DFa-sensitive individuals showed the inhibition of ISR and the accentuation of LSR on DFa-ID test.