Research on the indigenous intestinal microbiota of man was initiated well before the end of the 19th Century. The work continued at a slow but steady pace throughout the first half of the 20th Century. Findings from the effort had little impact on medicine and other aspects of human biology, however, until the 6th decade of the 20th Century. During that decade, research in the area was begun by eight groups of investigators, each of which was led by one or two senior scientists with great experimental talent, creativity and foresight. Their findings added new dimension to knowledge of the microbiota and initiated an explosion of interest in research in the field that has continued to the present day. The research of the groups during the 1960's is described in this review as a tribute to the senior scientists who had such critical impact on this important field of study.