The calcium-binding proteins Calbindin-D28k and calretinin are co-localized with dopamine in some of the midbrain dopaminergic neurons in the rat and monkey; the present study sought to examine the pattern of co-localization in the mouse. Double immunofluorescence staining procedures were used for tyrosine hydroxylase (a dopaminergic cell marker) and Calbindin-D28k or calretinin. Midbrain dopaminergic neurons were examined at four rostrocaudal levels, and the percentage of cells that contained both tyrosine hydroxylase and either of the two calcium-binding proteins was determined in nucleus A8 (retrorubral field), nucleus A9 (substantia nigra pars compacta, pars reticulata and pars lateralis) and nucleus A10 (nucleus paranigralis, ventral tegmental area, interfascicular nucleus, central linear nucleus). The two calcium-binding proteins were distributed similarly in midbrain dopaminergic neurons in the several nuclear groups that comprise nuclei A8, A9 and A10. The calcium-binding proteins were found in the majority (50-100%) of nucleus A10 neurons, whereas in nuclei A8 and A9 (except for the substantia nigra pars lateralis) less than 40% of the cells contained either calcium-binding protein. The pattern of co-localization in the mouse is similar to that reported for the rat and monkey. The calcium-binding proteins mark the population of midbrain dopaminergic neurons that are less vulnerable to degeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of Parkinson's disease.