AbstractCells of Saccharomyces carlsbergensis contain proteins assembling to crystals and bundles of tubules (tb) in the cyto‐ and karyoplasm by osmotic shock with hypertonic solutions. The cellular concentration of these proteins is regulated by oxygen pressure during growth. In cells grown at optimal aeration the protein level is low and crystals and tb cannot be induced. After a short period of O2‐limitation or anerobic growth conditions the protein concentration increases and induction of crystals and tb is possible.