The present invention provides a TNF-.alpha. production inhibitor containing a kavalactone as an active ingredient, which inhibitor has high safety, exerts an excellent effect of inhibiting TNF-.alpha. production, and is useful as a drug or an animal drug for preventing, ameliorating, or treating diseases such as cachexia attributed to cancer or infectious diseases, chronic rheumatoid arthritis, inflammatory diseases, osteoarthritis, systemic lupus erythematosus (SLE), rejection during bone marrow transplantation, multiple organ failure, AIDS, meningitis, hepatitis, and type-II diabetes. The present invention also provides a preventive, ameliorating, or therapeutic agent for diseases caused by abnormal production of TNF-.alpha., the agent containing a kavalactone as an active ingredient.