Human lysosomal elastase from polymorphonuclear leucocytes is inhibited by the cartilage bone marrow extract Rumalon. Separately, both the cartilage and the bone marrow extracts are able to inhibit the enzymatic activity by 73%, under saturating conditions. The mixture of the two extracts inhibits elastase by 93%. It is suggested that the two partners act as a cumulative inhibition mechanism and this phenomenon is emphasized in a general theoretical model for synergy of proteinase-directed inhibitors.