The activities of choline acetyltransferase (CAT) and glutamic acid decarboxylase (GAD), markers of cholinergic and GABAergic terminals, were measured in growing and adult Gunn rats, which possess an autosomal recessive gene for jaundice or kernicterus. In the olfactory tubercle, hippocampus, neostriatum, thalamus, and hypothalamus of the animals with kernicterus, the development of the cholinergic pathways was delayed, but by the adult stage it was normal, while there was practically no action on the innervation by GABAergic neurons, at least as indicated by the chemically measured parameters.