The syndrome had a rapid onset and was quite severe, but reversible upon stopping or lowering of the 5-fluorouracil (5-FU) dosage, or both. The importance of recognizing this syndrome was emphasized both from a clinical and a theoretical standpoint; the carcinomatous neuromyopathies may develop through a mechanism shown to be present in 5-FU toxicity, that is, RNA-DNA antagonism or competitive inhibition.