Previous studies have documented changes in skin reactivity after specific immunotherapy. The aim of this study was to evaluate the time course of this phenomenon after rush venom immunotherapy. According to the method of endpoint evaluation, the skin reactivity of 38 patients allergic to venom was studied 24 h before and after the end of a rush venom immunotherapy protocol (7 days). The results were compared with 13 controls. An early significant decrease in skin reactivity was documented (p < 0.001), which was not related to an increase in specific IgG. Thus, rush venom immunotherapy induces a very early decrease in skin reactivity.