In an in vitro experiment with pig inoculum, the main and interactive effects of type of protein and fibre on the concentrations of short-chain fatty acids (SCFA) and amines as the end products of fermentation and proteolysis were determined. The effects of inoculation with colonic digesta (C) sampled post mortem or with freshly voided faeces (F) as the sources of microflora, and of 24- vs 48-h periods of incubation, were also estimated. Potato protein and casein were fermented each with cellulose, pectin, or raw potato (resistant) starch. Each set of fermentation was repeated six times. The total SCFA concentration was greater after C than F fermentation, regardless of the substrates. It was the greatest after fermentation of both proteins with potato starch and greater after fermentation of all carbohydrates with casein than with potato protein. The largest concentrations of isobutyric and isovaleric acids were found after fermentation of casein with cellulose, but only with C (P = 0.040 and P = 0.030 for interaction, respectively). Also, a butyrogenic effect of potato starch was found only after C fermentation and was greater after 48 than 24 h. The total amines concentration after C and F fermentation of potato protein with all fibres was the same, while after C fermentation of casein it was affected by the type of fibre (P = 0.001 and P = 0.000 after 24 and 48 h, respectively). It was very high with cellulose, lower with starch and the lowest with pectin. It may be concluded that in vitro bacterial proteolysis is greatly affected by the interaction of type of protein and fibre. Forty-eight-hour fermentation with colonic digesta seems to be more discriminative than 24-h fermentation and colonic digesta is a more discriminative pig inoculum than faeces.