For a particular fusion-reactor blanket configuration, the changes in the tritium breeding ratio, i.e., in the number of tritium nuclei produced in the blanket per incident neutron, due to changes in nuclear cross-section data are calculated on the basis of linear perturbation theory. Results are presented for the changes in the breeding ratio due to changes in specific energy ranges of various partial cross sections of 6Li, 7Li, Nb, and C. The breeding ratio is found to be most sensitive to changes in the 7Li(n,n') α,t cross section, but the sensitivity to changes in this cross section is not large.