Complement components 1,2,3,4 and total complement hemolytical activity CH50 were studied in 39 patients with serve recurrent genital herpes simplex. The results show statistically significant and selective diminution of C4 (P>0.001) The other components were normal. C4 has a specific action against herpesvirus by itself or associated to some other elements over C4 failure, local or systemic disturbances alter the homeostasis of specific and nonspecific immune system, provking a disbalance host‐virus which would explain the recurrence.