The presence of an efficient uptake system for l-pyroglutamate was demonstrated in cultured glial cells originating from newborn rats. This compound is also transported by a high affinity uptake mechanism in neurons cultured from rat embryos cerebral hemispheres, but the V(max) is 6 times lower than for glial cells. It is shown that l-pyroglutamate like l-glutamate is preferentially transported by glial cells, but with a V(max) 40 to 60 times lower than for glutamate. The metabolism of l-pyroglutamate was also studied in cultured rat neuronal and glial cells, using l-[(3)H]pyroglutamate. Pyroglutamate, its metabolites and the various amino acids were separated by thin-layer electrophoresis. [(3)H]Pyroglutamate is more actively metabolised in glial cells than in neurons and glutamate is the main metabolite. Glutamate maximal specific activity is 4 times higher in glial than in neuronal cultures. It should also be noted that some [(3)H]pyroglutamate is transformed in [(3)H]GABA after longer incubation periods, but only in neurons. These results show the importance of glial cells for pyroglutamate uptake and metabolism in nervous tissue. They also suggest that pyroglutamate may interfere with glutamate neurotransmission in vivo.