Plasma zinc, copper, and selenium concentrations were determined in 129 full-term infants at birth and at the age of four months by electrothermal or hydride generation atomic absorption spectrometry. Of these, 49 infants were exclusively breast-fed (HM), 45 received various commercially available cow's milk formulae (F) and 35 infants were fed partially hydrolysed whey protein formula (PHF). The results were correlated with hematological, biochemical and somatic data. Plasma zinc values decreased from birth to the age of four months in all three groups (p < 0.001). The plasma Zn level of the babies fed PHF were similar to those of breast-fed infants, whereas in F-fed children the zinc values were significantly lower (PHF, 807 +/- 106; HM, 794 +/- 112; F, 725 +/- 111 micrograms l-1; all the measurements were performed at the age of four months). In infants fed PHF formula there was a negative correlation between plasma zinc and weight or height increments. In agreement with the literature, plasma copper and ceruloplasmin increased significantly within the first four months of life. The plasma copper content was similar in either feeding group. Plasma selenium was low at birth (40 +/- 9 micrograms l-1) and remained constant in breast-fed infants. In infants on PHF there was a steeper decline of plasma Se (20 +/- 6 micrograms l-1) than in infants fed cow's milk formula (29 +/- 9 micrograms l-1). Other parameters of the Se status showed a similar pattern. Despite the different zinc, copper, and selenium supply, plus presumedly different bioavailability, all the infants thrived.(ABSTRACT TRUNCATED AT 250 WORDS)