The distribution of the G alpha i-2 mRNA was investigated with in situ hybridization on tissue sections of the rat cerebral cortex. A non-radioactive method based on digoxygenin labelled cRNA was used for in situ hybridization. The G alpha i-2 mRNA was shown to be present predominantly in large neuronal shaped cells in laminae II-III. The ontogenic development of the expression of G alpha i-2 mRNA in the rat cerebral cortex was quantified using a solution hybridization RNAse protection assay. The abundancy of G alpha i-2 mRNA was shown to increase significantly from embryonic day 16 to adult age. The amount of G alpha i-2 mRNA in adult cerebral cortex of the rat brain was 23 amol/micrograms RNA. The distribution and ontogenic development of G alpha i-2 mRNA are discussed.