The number of starter bacteria in Cheddar cheese was increased approximately 2 or 8 times by supplementing the normal starter inoculum with starter-cell suspensions which had been incubated with lysozyme in the absence of salt. Lysozyme-treated cells were also introduced into chemically acidified cheese in an attempt to achieve ripening in the absence of a normal starter culture. The added starters did not interfere with normal cheese-making by producing acid. The lysozyme-treated starter cells were lysed when the curd was salted and lysis was detected by the release of cell-free DNA and an intracellular marker enzyme (dipeptidase) into the cheese matrix. Free amino acid concentrations in maturing cheeses were increased up to 3 times compared with control cheeses. The intensity of Cheddar flavour was not increased in starter cheeses by the presence of additional lysozyme-treated starter and no Cheddar flavour developed in chemically acidified cheese containing the lysozyme-treated cells. It is concluded that intracellular starter enzymes play no direct part in flavour formation, but produce breakdown products from which Cheddar flavour compounds may be formed by other unknown mechanisms.