Human lysosomal elastase from polymorphonuclear leukocytes is inhibited by the cartilage bone marrow extract Rumalon. Separately, the cartilage and the bone marrow extracts are able to inhibit the enzymatic activity by 73%, under saturating conditions. The mixture of the 2 extracts inhibits elastase by 93%. Apparently, 2 partners act as a cumulative inhibition mechanism. This phenomenon is emphasized in a general theoretical model for synergy of proteinase-directed inhibitors.