The concentration of epidermal growth factor (EGF) in mouse submaxillary gland displays a circadian variation, which can be phase-shifted by light-dark reversal and is abolished by superior cervical ganglionectomy (SCG). Such circadian variation persists in fasted animals. Peak concentrations occur during light hours and trough concentrations occur during dark, although peak concentrations in female animals occur 8 h in advance of the time when they are seen in male animals. The nocturnal fall can be reversed by a 1 h exposure to light presented during the normal dark period. SCG does not abolish the increase in submaxillary gland EGF concentrations to levels characteristic of the normal male that is seen following testosterone administration to female mice (who normally exhibit much lower EGF concentrations). Plasma EGF concentrations do not exhibit a circadian variation.