On the basis of some selected physical-chemical properties of a longissimus lumborum muscle taken from fatteners 24 hours after the slaughter, and, next, frozen at a temperature of –18°C, and stored during a period of 70 days, it was attempted to determine in what way the genotype of fatteners affected the development of some selected parameters assumed for the purpose of evaluation. The investigation material was taken from 80 fatteners showing a similar live weight of 105 kg, and being 180 days old. The animals were bred in an industrial pig fattening farm, under the similar environmental conditions of fattening. Each group of 20 heads of fatteners (10 sows and 10 barrows) represented one particular genotype. The muscle longissimus lumborum was evaluated on the basis of the following parameters: dry mater, water content, pH value measured 1 hr and 24 hours after the pigs were slaughtered, as well as on the 70th day of storing them (upon the defrosting of the samples investigated). The parameters: L*, a*, and b*, characterizing the muscle colour, were also determined. Values of the parameters investigated on the 70th day of storing the muscles, and determined after the samples were defrosted, showed significant differences (P≤0,05 and P≤0,01) compared with the parameter values determined in the groups and subgroups of fatteners. The most favourable values showed muscles of crossbreed fatteners [¾ PLW ¼ PL]. In the investigated groups and subgroups of fatteners, it was stated a statistically significant increase (P≤ 0.05 and P≤ 0.01) in the dry matter content in the defrosted muscle longissimus lumborum; additionally, this increase was confirmed with regard to samples of muscles taken from fatteners 24 hours after they were slaughtered. The only exception was a group of crossbreed fatteners [¼PLW¼PL¼Dur.¼Piet.]. In the paper, the differences were shown in the pH values and colour of fresh and defrosted L.L. muscles depending on the gender and genotype of animals the muscles were taken from. The results obtained prove that it is necessary to continue investigations on muscles taken from fatteners showing various genotypes, as is necessary to increase the number of parameters to be evaluated.