Plasma manganese concentrations of healthy women have recently been published in this journal (Hagenfeldt et al. 1973). It appears that these values (0.18–0.32 μg/100 ml) are several times higher than those found in plasma and serum by Cotzias et al. (1966) (0.0587 ± 0.0183 μg/100 ml). We determined by neutron activation analysis the serum manganese levels in 25 normal females and 25 normal males. No significant difference was found between the two groups. The overall concentration average was 0.057 μg/100 ml and the standard deviation 0.013 μg/100 ml. Higher values as reported by other investigators are apparently due to contaminations.