We have investigated accelerating the ripening of Pecorino Umbro cheese by adding crude cytoplasmic extract from Pseudomonas fluorescens, non-starter lactic acid bacteria (NSLAB) or cheese slurry. Microbiological and biochemical analyses and sensory evaluation were carried out on control and experimental cheeses over 28 d ripening. In the cheeses containing NSLAB or slurry, counts of mesophilic lactobacilli ranged from log 7·6 at day 1 to ∼log 8·6 cfu/g after 28 d ripening, ∼2 log cycles higher than in the control cheese. All the experimental cheeses contained higher levels than the control of total free amino acids and N soluble at pH 4·6 and in 120 g trichloroacetic acid/l. Compared with the control, higher aminopeptidase and dipeptidase activities were found in the cheeses containing NSLAB and slurry, and especially in those containing the Pseudomonas enzyme. The cheeses containing NSLAB or slurry were characterized by an accumulation of short peptides (Mr<2000) detected by FPLC. Although the cheese containing enzyme had an atypical flavour, the addition of mesophilic lactobacilli reduced from 60 to 28 d the ripening period of Pecorino Umbro cheese, without the appearance of off flavour.