Addition of human interleukin‐1 (IL‐1) to normal human gingival fibroblasts in culture stimulated the production of plasminogen activator (PA). This stimulation could be detected as early as 3 hours after addition of IL‐1, was dosedependent and inhibited by antibody directed against IL‐1. Additional observations suggest that IL‐1 increases PA production. These include: (1) an increase in both intra‐ and extracellular PA activity, (2) the dependence of increased PA activity on RNA and protein synthesis and (3) an increase in immunologically detectable PA molecules by immunoperoxidase staining. Since IL‐1 has been reported to be present in human gingival fluid and PA activity has been associated with connective tissue matrix alterations, the results presented here may provide some insight as to how immune events are linked to soft tissue destruction associated with