This review pertains the current knowledge concerned with the application of SCP in human and animal nutrition. General factors limiting the utilization of microbial proteins in human nutrition, such as toxicological barriers, nutritive value and functional properties, are discussed. Special attention is paid to several modern procedures of protein extraction from microbial cells, reduction of nucleic acids level as well as preparation of protein isolates. According to the data presented the latter can be considered as valuable protein substitutes. Significantly less nutritive problems are being concerned with the application of SCP in animal nutrition. Successful feeding experiments with chicken and pigs are discussed. Under these experimental conditions 10-20% of the protein in the feedstuff can be replaced by SCP. Moreover, several in Poland obtained protein-vitamin preparations are described. These originated from selected yeast and propionic acid bacteria grown in whey and its ultrafiltrates and can be considered as valuable food and feed supplements.