The levels of proteolytic activity in cell washes, lysates and pellets of C. pylori and gastric Campylobacter-like organisms isolated from humans and ferrets, respectively, have been studied using porcine mucus glycoprotein and bovine haemoglobin substrates. The total haemoglobin degrading activity, expressed by 10(12)-10(13) cfu of either organism, was no greater than 3 micrograms chymotrypsin equivalents. The mucolytic specific activity (rate of mucus peptide bond hydrolysis by bacterial protein) of the fractions tested from both organisms did not exceed 2nmol/min/mg protein. This value is 1000-fold lower than expected from published data. Electrophoretic profiles suggested that the mucolytic activity assessed by fluorimetry was insufficient to alter the quaternary structure of mucus and hence may not significantly contribute to the undermining of gastric mucus integrity.