The cerebellum-specific hexadecapeptide cerebellin has been localized by immunocytochemical means to the perikarya and dendrites of cerebellar Purkinje cells. Biochemical analysis using ion-pairing HPLC shows cerebellin to first appear 5 days after birth, whereafter levels rise to a maximum at 25 days postpartum, and then decline to stable adult values. This same pattern of development occurs with a lag of approximately 5 days for the major metabolite of cerebellin, des-Ser1-cerebellin. The immunocytochemical picture of cerebellin in developing Purkinje cells mirrors the biochemical data. These results show that cerebellins represent unique quantifiable markers for the investigation of Purkinje cell maturation and lend support to the feasibility of using unique endogenous peptides to chart neurodevelopment.