Metal complexing agents could exert antiinflammatory activity by inhibition of oxygen radical production, by inhibition of eicosanoid synthesis and by inhibition of metalloenzymes. We found a moderate antiedema activity of the iron (II)/iron (III)-chelator combination, o-phenanthroline/desferrioxamine, which could refer to an involvement of iron ions in the inflammatory reaction. The newly synthetized complexing agent ethylene-diimino-dibutyric acid caused weak antiedema and antivasodepressor effects which remain to be explained. Altogether, the in vivo effects of the metal chelators were rather weak. In vitro, only desferrioxamine produced a remarkable inhibition of two lipoxygenases.