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The aim of the study was to determine Se, Zn, and Cu concentrations in blood plasma and milk of lactating women from central Poland who were in different stages of lactation and to investigate the relationship between the content of trace elements in mothers' blood and concentrations of microelements in their milk. Se and Zn concentrations in blood plasma of mothers were the lowest and Cu was the highest on the first 4 d of lactation (colostrum, n = 43) and were found to be 34.9 ± 11.8 μg/L, 0.51 ± 0.13 mg/L, and 1.70 ± 0.55 mg/L, respectively. The highest plasma level of Se and Zn and the lowest content of Cu could be observed between d 10 and 30 of lactation (mature milk, n = 41), and were found to be 54.3 ± 14.6 μg/L for Se (p < 0.001), 0.76 ± 0.20 mg/L for Zn (p < 0.001), and 1.03 ± 0.30 mg/L (p < 0.001) for Cu.The results of Se, Zn, and Cu determination in breast milk samples demonstrate a pattern of decline in their concentration with advancing stages of lactation. We found out that Se, Zn, and Cu concentrations were the highest in colostrum (n = 43) and amounted to 24.8 ± 10.1 μg/L, 8.2 ± 2.8 mg/L, and 0.45 ± 0.11 mg/L, respectively. The content of all determined microelements declined significantly during the time of lactation. Statistically significant linear correlation was found between concentrations of Zn in blood plasma and milk in the first stage of lactation. Weak but statistically significant linear correlations were also found between plasma Se content in plasma and in transitional and mature milk of breast-feeding women.