1. The values for kallikrein, amylase and protein were determined in samples of saliva obtained from 220 girls aged 14–18 years.
2. The concentrations of protein and amylase and kallikrein activities (per ml of saliva) were considerably more variable in samples taken in the morning than those in the afternoon.
3. The median amylase activity was about two and a half times greater in the morning than that in the afternoon. No such differences were seen in the median values for protein or kallikrein.
4. Examination of the values for salivary kallikrein during the menstrual cycle showed that there was significantly greater activity during days 29–32 and 1–4 than during the rest of the cycle. This pattern was most marked in the morning values of kallikrein but not apparent either in the morning or in the afternoon values of protein or amylase.