Growth of Selenomonas rumitiantium HD4 in medium that contained 21 mM D-lactate was stimulated to varying degrees by 10 mM L-malate, 10 mm fumarate, and 2% (v/v) Aspergillus oryzae fermentation extract (Amaferm). Amaferm treatment caused the greatest growth stimulation. Initial uptake rates (30 s) and long-term uptake rates (30 min) Of D-lactate by whole cells of S. ruminantium were increased in the presence Of 10 mM L-malate. Amaferm (25 mul/ml) also stimulated long-term uptake rates Of D-lactate, whereas fumarate had no effect. Initial uptake Of D-lactate was depressed in the presence of fumarate or Amaferm. When either L-malate, fumarate, or Amaferm was included in the D-lactate growth medium, a homosuccinate fermentation resulted and an inverse relationship was observed between growth (protein synthesis) and succinate production. Recent research demonstrated that Amaferm contains L-malate, and this dicarboxylic acid may be involved in stimulating D-lactate utilization by S. ruminantium.