The postnatal development of some neurotransmitter parameters was measured in lateral geniculate body, superior colliculus and visual cortex of the rat. The following parameters were studied: (i) high-affinity uptake of L-glutamate or D-aspartate as markers for glutamergic neurons; (ii) high-affinity uptake of GABA, which reflects both glial and neuronal uptake of GABA; (iii) HA beta-alanine uptake as a marker for accumulation of GABA in glial structures; (iv) activity of glutamic acid decarboxylase which reflects GABAergic neurons; and (v) activity of choline acetyltransferase as a cholinergic marker. Km and Vmax were determined for high-affinity uptake of glutamate and GABA in newborn and adult animals. The possible glial influence on the uptake during development is discussed. In lateral geniculate body and visual cortex the HA glutamate uptake showed increasing activity from birth to adulthood, whereas in superior colliculus, the uptake was higher at birth, reaching a small significant peak after 12 days of age, and was then reduced to adult level. Km showed no such change between neonatal and adult animals. At birth, high-affinity GABA-uptake was similar to the adult level in superior colliculus and lateral geniculate body. In visual cortex, the uptake of GABA was 50% of adults. However, on day 15, the GABA uptake showed 2 to 3-fold higher activity in all regions when compared to adult level. Km for GABA uptake in neonatals and adults differed only in lateral geniculate body. High affinity uptake of beta-alanine was 50-80% lower in adults than in newborn rats. Glutamate decarboxylase activity, however, increased continuously in all 3 regions examined. This was true also for choline acetyltransferase.