The growth and botulinic toxin production of Clostridium argentinense G 89 HT in co-culture with Pseudomonas mendocina were studied using two culture systems with carbon sources of rapid and slow utilization. Growth with glucose in homogeneous co-culture presented a dual-phase progression, with the toxin produced in the slow-growing phase. The extended 50 h growth period of the second phase at low specific growth rate was attributed to the combined metabolization of glucose and a complex carbon source of the alginate type produced by P. mendocina under strongly reducing conditions. With dextrin, the co-culture grew at the lower specific growth rate (μ = 0.03 h⁻¹) for a period lasting 80 h. This fully enhanced the production of toxin with a specific toxicity 2.5 times higher than with glucose in a homogeneous system and 10.7 higher than that of C. argentinense G 89 HT single culture. The heterogeneous co-culture obtained with a dialysis membrane physically separating both bacteria (thereby eliminating the metabolic interaction) produced the lowest levels of growth and toxin of all the cases analyzed.