The previous findings that the group I and III mite allergens, and amylase present in mite faeces are hydrolytic enzymes has prompted a study to determine whether this material contains other enzymes which could be allergenic. Thus, spent growth medium devoid of whole Dermatophagoides pteronyssinus mites was shown to contain glucoamylase, lipase and lysozyme in addition to the cysteine protease, serine protease and amylase activities associated with the above allergens, respectively. All of these enzymes are probably associated with mite digestive processes. They were rapidly solubilised, heterogeneous with regard to charge (pI in the range 4–8) and demonstrated maximum biochemical activity in the neutral pH range. Three serine proteases were detected and comprised a chymotrypsin-like, a trypsin-like and an unclassified enzyme with pI of 4.1 and 5.3, 8.5 and 7.1, respectively. Only one cysteine protease was observed, which paralleled immunochemically identified Der p I in a variety of assays. It was shown to cleave at lysyl residues and could be inhibited by the specific cysteine protease inhibitor, E-64. The remaining serine proteases, glucoamylase, lipase and lysozyme represent potential allergens.