The investigations carried out on 626 growing pigs were designed to differentiate the extent to which the decreased quality of their meat resulted from the environmental conditions and that to which it was due to the genetic predispositions of the animals. The latter were evaluated on the basis of the presence of the Phi, Po2 and Pgd genes linked with the gene of halothan susceptibility to stress. The quality classes of meat were estimated by measurements of pH₁ and the IMP/ATP ratio (R₁) . The genotypes of the animals were determined on the basis of blood erythrocyte enzymes, phosphohexoisomerase (Phi) and phosphogluconate dehydrogenase (Pgd) and of the blood plasma protein, postalbumin-2 (Po2). There were 283 Phi^B-Po2^S-Pgd^A and Phi^B-Po2-Pgd^B haplotypes which amounted to 22.6% of their total number. The frequency of occurrence of the two haplotypes specified above in the configuration Phi-Po2-Pgd was the highest in pigs producing the PSE type of meat (45.7%), lower in animals with the DFD type of meat (30.3%) and the lowest in the group of pigs with normal meat (17.2%). Animals which produced PSE and DFD meat amounted to 37% of the examined population, whilst among them, 31.8% demonstrated genetic predispositions to meat defects.