A crude small particle pellet, obtained from postmitochondrial supernatant fractions of Saccharomyces cerevisiae , contains about half the ergosterol and phospholipid of crude cell homogenates. Most of the phospholipid of this pellet is in a “heavy” fraction which, with the aid of electron microscopy, shows membranous elements in addition to discrete particles. The “heavy” fraction, upon treatment with deoxycholate, can be freed of membranes, or, with ribonuclease treatment, ribosomes can be removed, leaving relatively clean membranes. The “heavy” fraction resembles the microsomes of animal cells, but contains considerably less lipids, including phospholipids, thus suggesting a less well-developed intracellular membrane system.