Amylase activity and isoenzyme pattern were determined in preterm human milk from 25 mothers during the first 55 days after delivery and from 25 mothers delivered at term. The diurnal variation in amylase activity and the variation during a feeding were studied in two mothers. There is a high amylase activity in preterm colostrum, which slowly decreases during the first 2 months. The individual variation in amylase activity is considerable. There is no difference in amylase activity in preterm and term human milk. The isoamylase of preterm milk is of the salivary type, just as in term milk. There is no great variation in amylase activity during a feeding or from one feeding to another.