Background: Capping protein (CP), a heterodimer of α and β subunits, is found in all eukaryotes. CP binds to the barbed ends of actin filaments in vitro and controls actin assembly and cell motility in vivo. Vertebrates have three isoforms of CPβ produced by alternatively splicing from one gene; lower organisms have one gene and one isoform. Results: We isolated genomic clones corresponding to the β subunit of mouse CP and identified its chromosomal location by interspecies backcross mapping. Conclusions: The CPβ gene (Cappbl) mapped to Chromosome 4 between Cdc42 and D4Mit312. Three mouse mutations, snubnose, curly tail, and cribriform degeneration, map in the vicinity of the β gene.