According to the present invention there is provided a preservative formulation for use in treating wood or other cellulosic formulations, said formulation comprising: at least one biocidal metal compound; at least one organic compound; and a carrier. Preferably, the preservative formulation is copper/(tebuconazole/propiconazole) in a ratio of about 1:3 w/w; the carrier is preferably aqueous or spirit-based.