Surgically implanted osmotic minipumps were used to apply dye or [3H]-muscimol locally to the nucleus ventralis lateralis or globus pallidus of the cat. Extent of distribution of dye or radioactivity was measured from the site of application. A uniform distribution (1.2-2.5 mm) of dye or radioactivity was found lateral, ventral, and posterior to the perfusion site. Distribution dorsal to the perfusion site (2.5-7.5 mm) is complicated by infiltration into areas damaged by the implanted cannula. Anterior distribution (approximately 5 mm) was extensive, apparently as a result of the dye or labeled compound entering major tracts or projection pathways. This study demonstrates that with the appropriate precautions, distribution of drug following perfusion into solid tissue of the brain can be restricted to a localized area. However, our results also suggest that the neuroanatomical features of the chosen area (and surrounding area) may play a significant role in altering the pattern and extent of drug distribution.