Muramyl dipeptide promised a new order of safety as well as efficacy, and we pursued its potential surgical applications with a sequence of experimental studies. The difficulty in organizing a proper surgical clinical trial with muramyl dipeptide as a surgical adjuvant was quite frustrating. Work in fundamental host defenses and related fields essentially came to a stop in the 1940s with the advent of antibiotics. The timing of bacterial challenge, if shifted from one week to the second week after immunostimulation, actually increased the death rate in our experimental animals. The percentage of monocytes so identified often corrected itself by the end of the third week after injury, returning to a subsequently defined normal range. On the other hand, in most patients who had lingering infection, that so-called “return to normal” took longer, and for some patients who proved to have ultimately fatal infections, their initially very low values remained so until death.