1. To identify the quantitative trait loci (QTL) affecting growth in chickens,we carried out QTL analysis on chicken growth traits using a population of 227F2 crosses between a Satsumadori (slow-growing, light-weight Japanese nativebreed used as a meat chicken) male and a White Plymouth Rock (early-maturing,heavy weight broiler). 2. We chose 78 microsatellite loci from 331 publiclyavailable on 14 linkage groups, with respect to their utility and location. 3.Two QTLs affecting body weight at 13 and 16 weeks were mapped at 220 cM onchromosome 1 (LOD scores, 2.8 and 4.5, respectively, at 13 and 16 weeks), and at60 cM on chromosome 2 (LOD scores, 6.2 and 8.1, respectively, at 13 and 16weeks). 4. The closest loci to the QTLs were LEI71 on chromosome 1 and LMU13 andMCW184 on chromosome 2. 5. The sites of the QTLs agreed closely with thosealready reported. Therefore, it seems likely that QTLs affecting growth ofchickens are located at these sites.