Aims: To investigate the hydrolysis of alpha (S1-), alpha (S0-), beta (B-), beta (A1-) and beta (A2)-caseins by 32 wild lactococci of different randomly amplified polymorphic DNA (RAPD) patterns, isolated from raw ewes' milk cheese, and the production of hydrophilic and hydrophobic peptides from whole casein by those strains. Methods and Results: Most strains hydrolysed all caseins, and degraded beta -caseins to a larger extent than alpha (S)-caseins, when the proteolytic activity of whole cells was determined by capillary electrophoresis. Higher levels of hydrophilic than of hydrophobic peptides were produced from whole casein by all strains, according to reverse-phase high performance liquid chromatography analyses. Conclusions: Cell envelope proteinases of most lactococci isolated from raw ewes' milk cheese were CEPII, CEPII/III or CEPIII (classification of Exterkate et al. 1993). A negative correlation was found between degraded alpha (S-) and beta -caseins and a highly positive correlation between hydrophilic and hydrophobic peptides. Significance and Impact of the Study: Fast acid-producing lactococci from raw ewes' milk cheese have considerable and diverse caseinolytic activities. Their peptide production patterns do not reveal serious risks of bitter-flavour defect in cheeses if used as components of dairy starters.