Lurcher in equilibrium ichthyosis chimeric mice were constructed to determine whether the death of cerebellar granule cells in lurcher mutants is caused by intrinsic or extrinsic factors. Quantitative analysis demonstrates that more lurcher granule cells survive in the chimeras than would have in the mutants themselves. Thus the granule cell death is an indirect consequence of the lurcher gene acting on some other cell type, probably the cerebellar Purkinje cells.