We analysed the expression of neuronal nitric oxide synthase (nNOS) in the mouse amygdalar basolateral complex (BLC) from embryonic day 15.5 to adult, using standard immunohistochemical methods. Our results indicate that each nucleus of the amygdalar basolateral complex displays a distinct nNOS expression pattern, which is established during the ontogenesis with minor changes in the adult. The basomedial nucleus (BM) exhibited the highest nNOS immunoreactivity in the basolateral complex, observable from early embryonic stages, whereas the lateral nucleus displayed the lowest level of immunoreactivity. The expression pattern for nNOS in the basolateral nucleus differed substantially from that of the lateral and basomedial nuclei, showing a slightly increase in the number of nNOS cells and neuropil staining from intermediate developmental until early postnatal stages. Two distinct types of nitrergic neurons, densely and lightly stained neurons, were observed in the developing basolateral complex. Both types of putative nitrergic neurons were unevenly distributed in the basolateral complex. On the basis of previous data regarding the colocalization between nNOS and GABA in the mouse claustrum, we suggest that nNOS expressing neurons in the basolateral amygdalar complex are both GABAergic and non-GABAergic.