Using two-colour flow cytometry >200 antibodies submitted to the 8th International Workshop of Human Leukocyte Differentiation Antigens (HLDA8) have been analyzed for their reactivity with resting and activated CD203c+ basophils. Four antibodies either non-reactive or weakly reactive with resting basophils exhibited an increased reactivity with basophils activated by anti-IgE-mediated cross-linking of the high affinity IgE receptor (FcεRI). These include antibod- ies against CD164 (WS-80160, clone N6B6 and WS-80162, clone 67D2), as well as two reagents with previously unknown specificities that were identified as CD13 (WS-80274, clone A8) and CD107a (WS-80280, clone E63-880). The activation patterns followed either the “CD203c-like” or “CD63-like” activation profile. The CD203c profile is characterized by a rapid and significant upregulation (of CD13, CD164, and CD203c), reaching maximum levels after 5- 15 min of stimulation. The phosphoinositide-3-kinase (PI3K)-specific inhibitor wortmannin inhibited the upregulation of these markers whereas 12-O-tetradecanoyl-phorbol-13-acetate (TPA) induced a rapid and FcεRI-independent upregulation within 1-2 min. In the CD63 profile, maximum upregulation (of CD63 and CD107a) was detected only after 20-40 min, and upregulation by TPA reached maximum levels after 60 min. In summary, our data identify CD13, CD107a, and CD164 as novel basophil-activation antigens. Based on time kinetics of upregulation, we hypothesize that molecules of the “CD203c group” and the “CD63 group” are linked to two different mechanisms of basophil activation. Using two-color flow cytometry> 200 antibodies submitted to the 8th International Workshop of Human Leukocyte Differentiation Antigens (HLDA8) have been analyzed for their reactivity with resting and activated CD203c + basophils. Four antibodies either non-reactive or weakly reactive with resting basophils implantation an increased reactivity with basophils activated by anti-IgE-mediated cross-linking of the high affinity IgE receptor (FcεRI). These include antibod- ies against CD164 (WS-80160, clone N6B6 and WS- 80162, clone 67D2) two reagents with previously unknown specificities that were identified as CD13 (WS-80274, clone A8) and CD107a (WS-80280, clone E63-880). The activation patterns followed either the “CD203c- like” or “CD63- like” activation The CD203c profile is characterized by a rapid and significant upregulation (of CD13, CD164, and CD203c), reaching maximum levels after 5- 15 min of stimulation. The phosphoinositide-3-kinase (PI3K) itor wortmannin inhibited the upregulation of these markers 12-O-tetradecanoyl-phorbol-13-acetate (TPA) induced a rapid and FcεRI-independent upregulation within 1-2 min. In the CD63 profile, maximum upregulation (of CD63 and CD107a) was detected only after 20-40 min, and upregulation by TPA reached maximum levels after 60 min. In summary, our data identify CD13, CD107a, and CD164 as novel basophil-activation antigens. Based on time kinetics of upregulation, we hypothesize that molecules of the “CD203c group” and the “CD63 group” are linked to two different mechanisms of basophil activation.