The effects of collection technique, storage container, and the duration and temperature of storage on selected nutrient concentrations in mature human milk were evaluated. Milk samples were collected during the fourth week of lactation from women 20-35 years of age by hand expression or suction. Greater volumes and fat concentrations were observed in milks collected by suction. Vitamin A, zinc, iron, copper, sodium, and protein nitrogen concentrations were not affected by storage of milk in either pyrex or polypropylene containers for up to 24 h. The storage temperature had a significant effect on protein nitrogen and ascorbic acid concentrations. These findings indicate that collection methods and storage procedures used for comparatively brief periods will affect the concentrations of selected nutrients of mature human milk. Specific recommendations are made for the collection and storage of milk.