Daily changes in components of breast milk with number of days of lactation after delivery were demonstrated by determining concentrations and distributions of several elements simultaneously. Concentrations of calcium, copper, magnesium, phosphorus, sulfur, and zinc were determined simultaneously by inductively coupled argon plasma-atomic-emission spectrometry (ICP) for whole milk and milk fractions (skimmed milk and whey) collected from 2 to 196 d postpartum from a healthy lactating mother. Calcium and phosphorus concentrations increased in transitional milk. With days postpartum, the other elements decreased from the highest concentrations in colostrum milk, the modes of decrease being characteristic for each element. Distributions of copper, iron, phosphorus, sulfur, and zinc in whey were determined on a gel-filtration column by HPLC with ICP detection (HPLC-ICP method). Distributions of the five elements and absorbance peaks at 254 and 280 nm changed dramatically day by day at the beginning (colostrum milk), resulting in constant distributions after 30 d (mature milk). These results suggest the important roles of daily changing constituents in breast milk, especially in colostrum milk, in the nutrition of the newborn. Several element peaks on a gel-filtration column were identified by comparison with standard samples.