Abstract: A method is disclosed for producing specially prepared bacteria of the genus Clostridium for producing solvents, enzymes, antibiotics, toxic proteins, or spores. Cell elongation to a critical length of at least about 3x is induced in an economical, abundantly available growth medium by serial subculturing under controlled conditions to effect synchronization of growth in the number of the cells and their effective mass and to produce a substantially homogeneous cell population. At least about 0.01M of a divalent cation such as calcium is added to the synchronized cells of critical length to stabilize the cells against death, lysis or aggregation. Where bacterial production of solvents is desired, cell division is inhibited by temperature shift or by chemical means when the cells reach a synchronized solventogenic state. Solvents produced by the specially prepared bacteria may be economically and readily recovered by conventional distillation procedures or the like.