The marker-assisted introgression of quantitative traits in crop plants is the topic of an ever-increasing number of reports (recent interrogation of bibliographic database using marker-assisted breeding or QTL as key words produced nearly 500 and 2500 hits respectively). Different papers based both on theoretical and experimental evidence, have also emphasized the limits of QTL-based breeding strategies when applied to quantitative traits. Among these limitations the molecular breeder may face are the precision, power and confidence associated to QTL detection, the important number of progenies to be manipulated when the number of QTL increases. A combination of marker-based and classical phenotype-based selections is often recommended. Our program of interspecific G. hirsutum / G. barbadense marker-assisted backcross selection, MABS, aims at transferring cotton fibre quality QTLs of G. barbadense into G. hirsutum. In the preceding seasons, the BC1, BC2 and BC2S1 served for 3 separate QTL analyses (Lacape et al., Crop Sc, in press). The pooled QTL data from the 3 populations revealed a total of 50 QTLs meeting permutation-based LOD thresholds (between LOD 3.2 and LOD 4.0 on a per-trait basis) for 11 fibre quality-related traits. When reducing the detection threshold to LOD 2.5, this total reached 80 QTLs. Individual phenotypic effects were essentially in the range of 5-15%, and rarely exceeded 20%. The direction of the effect of 70% of the QTLs was as expected from the parental value (better fibre length, strength and fineness conferred by the G. barbadense parent, and better maturity and colour conferred by the G. hirsutum parent alleles). A majority of the QTLs were co-localized within QTL-rich chromosome regions: when considering only the donor segments, for which positive contributions to fibre quality derived from the presence of the G. barbadense alleles, 19 regions on 15 different chromosomes were defined. Interestingly, 1/3rd (26 out of 80) of the QTLs (LOD