Spermidine/spermine N1-acetyltransferase (SSAT) is the key enzyme responsible for polyamine interconversion. SSAT mRNA (visualized by in situ hybridization histochemistry) was shown to have a wide but heterogeneous distribution in the central nervous system (CNS) at both regional and cellular levels. The highest labelling was observed in hippocampus (pyramidal and polymorph neurons) and olfactory bulb. Present data suggest that polyamine metabolism in the CNS is not homogeneous but rather that the preferential production of a polyamine species is region- and cell type-specific.