Good sporulation was induced in batch culture using carbon sources that have in common the effect of reducing growth rate. We have recently demonstrated that sporulation of Clostridiwn thermosaccharolyticum does not occur endotrophically but requires an exogenous source of carbon and energy (2). It was also demonstrated that sporulation occurred under conditions of restricted growth. Pheil and Ordal (3) had previously demonstrated that a medium containing L-arabinose, as the carbon and energy source, supported sporulation. A reexamination of growth and sporulation in this medium demonstrated that growth was restricted because arabinose was utilized slowly. The specific growth rates in arabinose-and glucosecontaining media were 0.105 and 0.578, respectively. This then raised the question of whether other carbon sources, which were utilized less