Quantitative levels of resident aerobic and anaerobic bacteria of the face, show a characteristic age-related pattern. The density of anaerobic diptheroids and surface aerobic micrococci is higher in infancy than in early childhood. At puberty the quantity of organisms increases, with significantly higher levels achieved in late adolescence. Maximum counts are attained in early adulthood and remain constant until old age when a trend toward lower numbers occurs. These changes seem to correlate with the production of sebum.