GD3 and GM2 synthases act on ganglioside GM3 at the branching point of the pathway of synthesis of gangliosides in which the "a", "b" and "c" families are produced. The relative activities of these enzymes are important for regulating the ganglioside composition of a given tissue. In the present work, we report the cloning and characterization of a chick GD3 synthase cDNA. The cloned cDNA directed the synthesis of a functionally active enzyme in transiently transfected CHO-K1 cells and was highly homologous to mammalian GD3 synthases. In Northern blot experiments the cDNA detected a single specific GD3 synthase mRNA of about 9.0 kb both in the chicken brain and retina. The abundance of the specific mRNA transcript declined steadily from E7-E9 to very low values around PN2. The levels of enzyme activities measured at the same developmental stages roughly followed the changes of specific mRNA levels in both tissues. In situ hybridization of embryonic neural retina cells in culture showed that both glial- and neuron-like cells expressed the specific GD3 synthase mRNA, although with different intensities. Results indicate that transcription and/or stability of the specific GD3 synthase mRNA constitute a level of control of the expression of GD3 synthase and indirectly of the ganglioside composition in the developing chicken central nervous system (CNS).