Abstract The interrelations of the seven elements, calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), phosphorus (P), copper (Cu), zinc (Zn), and cadmium (Cd) in human breast milk were examined in Japanese mothers to clarify the effects of Cd exposure on these important elements for infant growth. Breast milk and urine samples were obtained from 68 mothers, aged 19–38 years, at 5–8 days postpartum. The concentrations were determined by inductively-coupled plasma atomic emission spectrometry for Ca, Mg, Na, K, P, by flame atomic absorption spectrophotometry for Cu and Zn, and by flameless atomic absorption spectrophotometry for Cd. Geometrical mean Cd concentrations were 0.28 (geometrical standard deviation=1.82) μg/l in breast milk and 1.00 (1.93) μg/g creatinine in urine. Among the above elements only Cd concentration in breast milk was significantly correlated with urinary Cd concentration ( r=0.451, P<0.001). Significant positive correlations were found between Cu and Ca ( r=0.500, P<0.001), Cu and Mg ( r=0.378, P<0.01), and Zn and Mg ( r=0.355, P<0.01) in breast milk. Cd concentration in breast milk showed an inverse relationship with Ca concentration in breast milk ( r=−0.248, P<0.05). These results indicate that the Cd concentration in breast milk closely reflects Cd body burden, with increased Cd in breast milk possibly affecting Ca secretion in breast milk.