Over the last 10 years, a significant body of evidence has emerged indicating that chemically diverse classes of naturally-occurring substances derived from higher plants are of potential interest for therapeutic interventions in several inflammatory diseases. Part I of this review article focuses on our current knowledge of the mechanisms by which a large range of plant-derived constituents interfere with three relevant targets involved in the inflammatory process, namely arachidonic acid metabolite pathways, nitric oxide and NF-kappaB, and discusses their potential therapeutic use in the management of relevant inflammatory diseases.