"Inborn errors of metabolism" and "chemical individuality", two ideas of Sir Archibald Garrod briefly revisited 50 years after his death.

Two ideas of Sir A. Garrod, "chemical individuality" (1902) and "inborn errors of metabolism" (1908) have proved fundamental for the development of medical knowledge. The latter idea was more fortunate than the former which, however has been extremely heuristic. On the other hand the two ideas are not entirely independent of each other: in fact, a third Garrodian concept, "inborn factors in disease", represents a significant link between them. "Inborn errors of metabolism" revived the laws of genetics and opened the way to interpretation of the molecular diseases with all their inherent practical modern implications (neonatal screening, prenatal diagnosis, and in perspective, genetic engineering). "Chemical individuality" still constitutes a valid premise for knowledge of biological individuality (in other words, the "biological ego") fundamentally programmed for conservation of self and for continuous discrimination of self versus non-self.