Good quality smear-ripened cheeses, such as Tilsit, are defined by the development of a bacterial smear on the surface which imparts characteristic flavour and distinctive red-orange colour to the cheeses. The objective of this study was to characterise proteolysis in the surface layers by taking sequential samples (similar to2 mm) from the surface up to 2 cm depth and thus to ascertain the extent to which enzymes from smear microorganisms penetrate into the cheese curd. Moisture increased from 36% at the surface to 43% at the core. pH decreased from 8.7 at the surface to similar to6 in the core. Levels of pH 4.6-soluble nitrogen expressed as a percentage of total nitrogen generally decreased as sample depths increased. Urea-PAGE showed beta-casein was strongly degraded within the upper few millimetres where the pH was higher thus enhancing plasmin activity. RP-HPLC chromatograms revealed greater hydrolysis of peptides in the surface layers. Concentrations of free amino acids were highest in the first slice (0-2 mm) and were lowest in the core. Most extensive proteolysis was seen in the first 5-10 mm from the surface. At levels deeper than this, the smear had little effect on proteolysis. This conclusion reflects the fact that, unlike volatile flavour compounds, enzymes diffuse very little from the surface of smear-ripened cheeses.