Carcass and meat quality traits were studied in 94 barrows of known HAL-1843 genotype (homozygote - - and heterozygote - +) from three crosses slaughtered at 90 kg and 120 kg live weight. Crosses A and B were produced from sires of which 0·5 of the genes were from a heavy-muscled × Large White line and 0·5 from pure Pietrain (A) or Duroc (B). Sows for both A and B were from a hyperprolific Large White × Landrace line and this latter line produced the pigs for cross C (control). The carcasses from cross A which were sired from boars having 0·75 of their genotype from heavy-muscled genetic lines had higher killing-out proportion, better conformation scores, greater loin depth and loin area, less carcass length and bone content, and greater lean proportion compared with cross C. The carcasses from cross B, with roughly 0·25 of Duroc genes had a significantly higher backfat thickness than either cross A or C. However their composition was not significantly different from C, since the higher backfat was counter-balanced by their better conformation. Carcass and lean weight distribution was more favourable in crosses A and B, which had significantly higher economic yields than cross C. The halothane genotype did not have a significant effect on fatness and carcass composition, although the heterozygote showed a significantly greater muscle depth. In addition, no significant effect of the halothane gene on carcass and lean weight distribution was observed. In relation to the light group of carcasses (72·8 (s.e. 4·4) kg), the heavy group (100·1 (s.e. 2·7) kg) had greater killing-out proportion, better conformation, longer carcasses, higher fatness and greater loin depth and area. These genetic lines showed a 9·6 g/kg increase in fat and a 6·1 g/kg decrease in lean for every 10 kg of increasing slaughter weight. With the slaughter weight increase the longissimus dorsi muscle became less pale due to a higher muscle pigment concentration, and the backfat had a higher proportion of oleic and lower proportion of linoleic and palmitic fatty acids. The halothane genotype had a significant effect on meat quality. The heterozygote produced much paler, softer and more exudative meat. However, the effect of cross and carcass weight was not significant for meat quality measurements determining pale, soft and exudative meat.