The present study deals with the developmental behaviour of cytosolic and membrane-bound gangliosides, especially the alkali labile species, in rabbit cerebrum and cerebellum from birth to 6 months of life. At all ages the amount of cytosolic gangliosides was less than 0.5% of total gangliosides. The proportion of alkali labile gangliosides on the total membrane-bound ganglioside content and the profile of the individual alkali labile gangliosides during postnatal life were different in cerebellum and cerebrum. In cerebellum the proportion of alkali labile gangliosides progressively increased from 4.6% at birth to 16.7% at 6 months; in cerebrum the proportion decreased from 8.9% at birth to a minimum of 5.5% at 10 days, then slowly increased up to 8.1% at 6 months. All the major alkali labile gangliosides in cerebellum, especially O-Ac-GT1b and O-Ac-GQ1b, tended to accumulate during postnatal life. In cerebrum only two alkali labile gangliosides, namely O-Ac-GT1b and a species not yet identified, increased starting from the 10th day of life, while the other ones progressively diminished after birth.