Kainate (KA) is a potent neuroexcitatory agent that induces seizure and brain damage syndromes with increasing efficiency during maturation. It has been suggested that the selective neuronal damage induced by KA may result not only from its depolarizing actions, but also from intracellular accumulation of Ca2+. The effects of KA are mediated by specific high-affinity receptors, enriched in the hippocampus. Members of this class of receptors, GluR5 and GluR6, have been characterized by cDNA cloning. Ca2+ permeability of the GluR6 receptor is determined by editing in the corresponding RNA. We report here a rapid PCR-based approach to assess in all experimental conditions the levels of GluR5 and GluR6 editing in the transmembrane TMII region. We show that editing in both GluR5 and GluR6 RNA is developmentally regulated and that different regions of the adult rat hippocampus demonstrate distinct levels of GluR6 editing.