We review efforts to further understand the development and nature of sensory processing mechanisms in the cat visual cortex. In vitro autoradiographic and homogenate assay techniques have been employed to determine the laminar distribution and characteristics of various neurotransmitter and neuromodulator receptor populations during postnatal development. Each receptor population shows a distinct laminar-specific pattern of binding, which, in most cases, is age-dependent. Changes in receptor number and affinity are also observed during postnatal development. These findings indicate that major alterations in the basic chemical circuitry of cat visual cortex are a normal feature of postnatal maturation and may play a role in plasticity mechanisms.