Improvements in the porcine genetic map and availability of resource families tostudy performance traits in pigs have made it possible to re-examine previousfindings that linked certain traits to genes or chromosomal regions. Previousstudies suggested that chromosomes 4 and 7 may be associated with growth andperformance traits. To confirm these previous results, an intervalmapping-regression approach was used to determine whether quantitative traitloci (QTL) exist in the Iowa State University reference/resource families.Traits measured were birth weight; body weight at 21 d; weaning weight (weightat 42 d); average daily gain; backfat at the first, 10th, lumbar, and last ribsand average backfat thickness; loin eye area; meat color; marbling; andfirmness. The total number of F2 pigs used ranged from 241 to 330 and came fromfive Chinese x American resource families. Five markers (S0001, SW871, S0175,S0214, and SW445) were genotyped and mapped on chromosome 4, and so were 10markers (S0064, tumor necrosis factor alpha [TNFalpha], S0102, S0078, S0158,S0066, SW304, SW1083, S0101, and S0212) on chromosome 7. Data were analyzed foreach family (breed cross) separately and were also pooled. Experiment-wisethresholds were used to determine significance. Suggestive evidence of QTL onchromosomes 4 and 7 was observed for several traits in pooled and individualfamily analyses. Suggestive evidence of a QTL with a relatively large effect foraverage daily gain was detected on chromosome 4 in the pooled analysis.Significant (P < .05) evidence for QTL was seen on chromosome 7 for 10th-rib,last-rib, and average backfat thickness in the pooled data set in a region ofthe chromosome that was near TNFalpha. These results verify in part thatchromosomes 4 and 7 contain QTL for growth and carcass traits.