Every year, consumers' demands on the quality of the product increase, and the question of the safety of the feed components used becomes more and more important. The aim of this study was to determine the effects of guar meal, with different protein content on the values of selected biochemical indices of dehydrated blood of pigs. The pigs were divided into four groups. The animals in control group (1) were fed a diet containing soybean protein (SBM) as the main protein source. In the diets for experimental groups 2, 3 and 4, SBM protein was replaced with guar meal protein at 25%, 50% and 75% respectively. The material for the study came from 24 crossbred pigs that were fed the selected diets for 92 days. One week before expected slaughter, blood was drawn from the pigs in all groups for biochemical analyses. The use of a different protein source had no significant influence on the changes in the investigated biochemical parameters in the blood of fattening pigs from the different experimental groups. The pigs were slaughtered according to the usual procedure in meat plants. Immediately after slaughter, sections of the liver,  were taken during carcass cutting. For the prepared specimens, a morphological as-sessment of the. Based on the investigations carried out and the results obtained, it can be concluded that the use of 50% and 75% guar meal protein as a substitute for SBM protein has negative effects on the pig organism. Most of the morphological changes were found in the livers of animals fed diets with a higher content of guar meal protein. The results of the study thus show that the evaluation of the biochemical indices in serum alone does not provide a complete picture of all changes in the organism of pigs under the influence of guar protein; only in combination with the results of the morphological examinations of the internal organs do they provide complete information about the health status of the animals.