To study the regulation and function of the growth-associated protein B-50/growth-associated protein-43 (mol. wt 43,000) in Xenopus laevis, B-50/growth-associated protein-43 complementary DNAs were isolated and characterized. The deduced amino acid sequence revealed potential functional domains of Xenopus B-50/growth-associated protein-43 that may be involved in G-protein interaction, membrane-binding, calmodulin-binding and protein kinase C phosphorylation. The expression of B-50/growth-associated protein-43 at the RNA and protein level during development was investigated using the Xenopus complementary DNA and the monoclonal B-50/growth-associated protein-43 antibody NM2. The antibody NM2 recognized the gene product on western blot and in whole-mount immunocytochemistry of Xenopus embryos. Moreover, visualization of the developmentally regulated appearance of B-50/growth-associated protein-43 immunoreactivity showed that this mode of detection may be used to monitor axonogenesis under various experimental conditions. In the adult Xenopus, XB-50/growth-associated protein-43 messenger RNA was shown to be expressed at high levels in brain, spinal cord and eye using northern blotting. The earliest expression detected on northern blot was at developmental stage 13 with poly(A) RNA. By whole-mount immunofluorescence, applying the confocal laser scanning microscope, the protein was first detected in embryos from stage 20, where it was expressed in the developing trigeminal ganglion. Also later in development the expression of the B-50/growth-associated protein-43 gene was restricted to the nervous system in Xenopus, as was previously found for the mouse. In conclusion, we find that XB-50/growth-associated protein-43 is a good marker to study the development of the nervous system in Xenopus laevis.