To examine diurnal patterns of milk zinc concentrations, midfeed samples were obtained at approximately 6 a.m., 9 a.m., 12 noon, 3 p.m., 6 p.m., and 9 p.m. on a total of 29 days from 16 lactating women. Within-feed patterns were examined in 32 subjects with analysis of samples of fore-, mid-, and hindmilk from a total of 175 feeds. There were no significant differences between means for any of the diurnal intervals or between means for fore-, mid-, and hindmilk samples. These results indicate that milk zinc concentrations of random samples of human milk collected at any time of the day or of the feed can be accepted as representative for that day.