92% of the cellular proteins from the osmotically fragile strain Sacch. cerevisiae 211 (MATa srbl srb2 tsl) were extracted by one passage in a high pressure disintegrator at 650 atm. After isoelectric precipitation, 60.1% of the proteins were isolated. The protein extract was rich in proteins (60-70%) but also contained 12-13% nucleic acids and 13-14% carbohydrates. Mild conditions were created for simultaneous reduction of nucleic acids and carbohydrates in the lysate prior to precipitation of proteins. Under these conditions the amount of nucleic acids in the protein extract was reduced to 2%, and that of the carbohydrates to 5.7%. As a result of the whole procedure on a pilot scale, 11 culture of Sacch. cerevisiae 211 grown in molasses based nutritional medium yielded 1 g protein extract. The applicability of this protein extract for nutritional purposes was demonstrated by determination of its amino acid composition, acute toxicity tests with Tetrahymena pyriformis and short-term animal nutrition tests. The results showed that the protein extract is a suitable source of SCP for nutritional purposes.