Interspecies hybrids between Père David's deer (Elaphurus davidianus) and red deer (Cervus elaphus) have proved to be a powerful resource in the search for quantitative trait loci (QTL) in deer. Several regions of the genome with significant effects on live weight and growth rates in backcross hybrids were detected. These include putative QTL for 6-month live weight (LOD 3.90) on linkage group 12, for 14-month live weight (LOD 3.19) on linkage group 1, three putative QTL for growth rate from 3 to 6 months (LOD 4.19 on linkage group 12, LOD 3.92 on linkage group 12, and LOD 3.34 on linkage group 5). In addition, linkage groups 20 and 1 appear to be associated with live weight traits between 9 and 16 months. The variance in traits explained by these QTL ranged between 5.3% and 11.2%. Allele substitution with Père David's alleles at different loci had both positive and negative effects on live weights and growth rates.