Neurological mutant mice have yielded an early and continuously rich resource for studying the role of genes in the developing cerebellum. Experimentally produced chimeric mice, containing mixtures of genetically normal and mutant cells, provided a means of deducing the primary site of gene action and studying cell interactions in these mutant cerebella. Recently, three mutant genes, reeler, weaver, and staggerer, have been cloned and their gene products identified. These three genes have been examined earlier by the chimera technology. Here, we review the chimera studies in the light of what we now know to be the products of these mutant genes.