Two tests have been undertaken to investigate the influence of feeding microbial biomasses to pigs. No alterations of the fat parameters characterizing the fat stability were observed. All the values obtained are in a normal range. Increases in heptadecenic acid were detected dependent on the content of microbial biomasses in the feed and its fat content. The alterations are mainly in a normal range or slightly beyond it. In nature odd-numbered fatty acids are ubiquitous. Uptake and storage suggest that the organism reacts to an increased offer of C17-fatty acids with an accelerated decomposition of these fatty acids or/and with inhibition of their endogenous synthesis. The results are discussed in comparison with those of literature.