The present study was conducted to further examine the observed phenotypic differences in the sensitivity to chronic manganese exposure. Albino mice (NMRI-IVIC strain) and C57BL/6 black mice were divided into two groups. One group of mice was given daily i.p. injections of manganese during 9 weeks. The control group of each strain was treated with saline. After treatment, we examined their spontaneous motor activity. Manganese administration did not alter the measured locomotor activity in any of the strains. We also determined the concentrations of several monoamines and their metabolites, in the substantia nigra (SN), corpus striatum (CS) and locus coeruleus (LC), by High Pressure Liquid Chromatography with electrochemical detection. In our study, the administration of Mn did not change any of the brain amines analyzed. However, it was evident that there were striking differences in the endogenous levels of monoamines between both strains: dopamine concentrations in SN and CS of C57 mice were markedly lower than those present in albino mice. Dihydroxy phenyl acetic acid levels were higher in CS of C57 mice; whereas there was no difference in the homovanillic acid content. The concentrations of adrenalin and scrotonin were lower in the CS of C57 mice, but did not differ in SN and LC. We found higher levels of noradrenaline in the LC and CS of C57 mice. We conclude that in spite of the observed differences in the amine concentrations of the two strains, C57 black mice were not more susceptible to the effects of manganese, than the albino mice strain studied.