We have found that cells in the ferret thalamic reticular nucleus (TRN) express brain nitric oxide synthase (bNOS) in a transient pattern during early postnatal development. Similar to our previous findings in the lateral geniculate nucleus (LGN), bNOS expression in the TRN is first observed at postnatal day 7 (P7) and continues to P35. Quantitative measures show a significant change in the relative numbers of bNOS+ cells from P7-P35, and suggest there is a transition in morphology from a bipolar shape with two primary dendrites, to a more complex, multipolar arrangement. During TRN development, the pattern of bNOS expression shifts from the somatodendritic localization seen during the first postnatal month to expression within axon fibers in the adult. Expression of bNOS within TRN cells demonstrates an additional source of nitric oxide in the developing visual thalamus, perhaps indicating a common function for thalamic nitergic neurons as cellular mediators in the establishment of central topography both in the LGN and the TRN.