The study was conducted to determine if the response of swine cecal microflora to lactitol (beta-D-galactopyranosyl-(1-->4)-D-sorbitol; 3 mmol/L) varies when fermenting low (LF) or high fiber (HF) predigested diets. The inoculum was collected from four sows fitted with cecal cannulas, pooled, buffered and dispensed in 27 vessels under anaerobic conditions. The LF or HF predigested diets were used as substrate in two separate experiments. In each trial nine vessels were used as controls (C) without feed addition, nine received predigested feed (LF or HF) and the remaining nine vessels received the same amount of feed with the supplementation of lactitol (LF+L or HF+L). Lactitol (L) significantly lowered pH and the acetic to propionic acid ratio in the first 8 h of fermentation in both experiments (P < 0.05). At 4 and 8 h, the addition of lactitol reduced ammonia by 100 and 84% in LF+L and by 56 and 38% in HF+L (P < 0.05). In addition, LF+L and HF+L diets gave higher short-chain fatty acid energy yields by 70 and 40% than LF and HF, respectively (P < 0.05). Two bacterial growth models (logistic and Gompertz) were tested to fit gas production data. The Gompertz equation provided a better fit than the logistic model to gas production data for both LF and HF experiments. Lactitol reduced culture lag time in both experiments by approximately 50%, but it increased gas production rate and maximum gas production by approximately 60% only when the microflora was fermenting the LF predigested diet (P < 0.05). No difference in the duration of the exponential phase due to lactitol was observed in either experiment. Our results indicate that lactitol may be an interesting additive to animal feeding. It controlled harmful fermentation processes and stimulated short-chain fatty acid production to a greater extent in low than in high fiber diets, suggesting an improved fermentation of low fiber feed carbohydrates and eventually an increased availability of short-chain fatty acids for the host.