In an experimental cross between Meishan and Dutch Large White and Landracelines, 619 F(2) animals and their parents were typed for molecular markerscovering the entire porcine genome. Associations were studied between thesemarkers and two fatness traits: intramuscular fat content and backfat thickness.Association analyses were performed using interval mapping by regression undertwo genetic models: (1) an outbred line-cross model where the founder lines wereassumed to be fixed for different QTL alleles; and (2) a half-sib model where aunique allele substitution effect was fitted within each of the 19 half-sibfamilies. Both approaches revealed for backfat thickness a highly significantQTL on chromosome 7 and suggestive evidence for a QTL at chromosome 2.Furthermore, suggestive QTL affecting backfat thickness were detected onchromosomes 1 and 6 under the line-cross model. For intramuscular fat contentthe line-cross approach showed suggestive evidence for QTL on chromosomes 2, 4,and 6, whereas the half-sib analysis showed suggestive linkage for chromosomes 4and 7. The nature of the QTL effects and assumptions underlying both modelscould explain discrepancies between the findings under the two models. It isconcluded that both approaches can complement each other in the analysis of datafrom outbred line crosses.